Reduce number of queries in epic_issues services specs

What does this MR do?

Contribution based on data extracted from the rspec profiling project.

Modifies the specs files within ee/spec/services/epic_issues to reduce DB hits by replacing the helper let with let_it_be where possible.

Queries saved: 11479

1. ee/spec/services/epic_issues/create_service_spec.rb

• Number of queries: 13252 -> 6251
• Total Time: 00:31.563 -> 00:16.997

TEST PROF INFO - Before

 EVENT_PROF='sql.active_record' bin/rspec ./ee/spec/services/epic_issues/create_service_spec.rb
Running via Spring preloader in process 53066
[TEST PROF INFO] Activating EVENT_PROF with `Spring.after_fork`
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}
[TEST PROF INFO] EventProf enabled (sql.active_record)
.....................................................[TEST PROF INFO] EventProf results for sql.active_record

Total time: 00:15.430 of 00:31.563 (48.89%)
Total events: 13252

Top 5 slowest suites (by time):

EpicIssues::CreateService (./ee/spec/services/epic_issues/create_service_spec.rb:5) – 00:15.430 (13252 / 53) of 00:31.563 (48.89%)

Finished in 34.94 seconds (files took 3.65 seconds to load)
53 examples, 0 failures

TEST PROF INFO - After

EVENT_PROF='sql.active_record' bin/rspec ./ee/spec/services/epic_issues/create_service_spec.rb
Running via Spring preloader in process 24095
[TEST PROF INFO] Activating EVENT_PROF with `Spring.after_fork`
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}
[TEST PROF INFO] EventProf enabled (sql.active_record)
.....................................................[TEST PROF INFO] EventProf results for sql.active_record

Total time: 00:07.576 of 00:16.997 (44.57%)
Total events: 6251

Top 5 slowest suites (by time):

EpicIssues::CreateService (./ee/spec/services/epic_issues/create_service_spec.rb:5) – 00:07.576 (6251 / 53) of 00:16.997 (44.57%)



Finished in 19.98 seconds (files took 3.26 seconds to load)
53 examples, 0 failures

2. ee/spec/services/epic_issues/destroy_service_spec.rb

• Number of queries: 1725 -> 698
• Total Time: 00:06.064 -> 00:03.757

TEST PROF INFO - Before

EVENT_PROF='sql.active_record' bin/rspec ./ee/spec/services/epic_issues/destroy_service_spec.rb
Running via Spring preloader in process 73127
[TEST PROF INFO] Activating EVENT_PROF with `Spring.after_fork`
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}
[TEST PROF INFO] EventProf enabled (sql.active_record)
.........[TEST PROF INFO] EventProf results for sql.active_record

Total time: 00:02.461 of 00:06.064 (40.58%)
Total events: 1725

Top 5 slowest suites (by time):

EpicIssues::DestroyService (./ee/spec/services/epic_issues/destroy_service_spec.rb:5) – 00:02.461 (1725 / 9) of 00:06.064 (40.58%)



Finished in 9.09 seconds (files took 3.19 seconds to load)
9 examples, 0 failures

TEST PROF INFO - After

EVENT_PROF='sql.active_record' bin/rspec ./ee/spec/services/epic_issues/destroy_service_spec.rb
Running via Spring preloader in process 9610
[TEST PROF INFO] Activating EVENT_PROF with `Spring.after_fork`
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}
[TEST PROF INFO] EventProf enabled (sql.active_record)
.........[TEST PROF INFO] EventProf results for sql.active_record

Total time: 00:01.081 of 00:03.757 (28.78%)
Total events: 698

Top 5 slowest suites (by time):

EpicIssues::DestroyService (./ee/spec/services/epic_issues/destroy_service_spec.rb:5) – 00:01.081 (698 / 9) of 00:03.757 (28.78%)



Finished in 6.76 seconds (files took 3.14 seconds to load)
9 examples, 0 failures

3. ee/spec/services/epic_issues/list_service_spec.rb

• Number of queries: 1471 -> 812
• Total Time: 00:06.065 -> 00:04.137

TEST PROF INFO - Before

EVENT_PROF='sql.active_record' bin/rspec ./ee/spec/services/epic_issues/list_service_spec.rb
Running via Spring preloader in process 94729
[TEST PROF INFO] Activating EVENT_PROF with `Spring.after_fork`
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}
[TEST PROF INFO] EventProf enabled (sql.active_record)
....[TEST PROF INFO] EventProf results for sql.active_record

Total time: 00:02.119 of 00:06.065 (34.94%)
Total events: 1471

Top 5 slowest suites (by time):

EpicIssues::ListService (./ee/spec/services/epic_issues/list_service_spec.rb:5) – 00:02.119 (1471 / 4) of 00:06.065 (34.94%)



Finished in 9.01 seconds (files took 3.21 seconds to load)
4 examples, 0 failures

TEST PROF INFO - After

EVENT_PROF='sql.active_record' bin/rspec ./ee/spec/services/epic_issues/list_service_spec.rb
Running via Spring preloader in process 6174
[TEST PROF INFO] Activating EVENT_PROF with `Spring.after_fork`
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}
[TEST PROF INFO] EventProf enabled (sql.active_record)
....[TEST PROF INFO] EventProf results for sql.active_record

Total time: 00:01.339 of 00:04.137 (32.38%)
Total events: 812

Top 5 slowest suites (by time):

EpicIssues::ListService (./ee/spec/services/epic_issues/list_service_spec.rb:5) – 00:01.339 (812 / 4) of 00:04.137 (32.38%)



Finished in 7.44 seconds (files took 3.28 seconds to load)
4 examples, 0 failures

4. ee/spec/services/epic_issues/update_service_spec.rb

• Number of queries: 3650 -> 858
• Total Time: 00:09.912 -> 00:03.781

TEST PROF INFO - Before

EVENT_PROF='sql.active_record' bin/rspec ./ee/spec/services/epic_issues/update_service_spec.rb
Running via Spring preloader in process 11239
[TEST PROF INFO] Activating EVENT_PROF with `Spring.after_fork`
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}
[TEST PROF INFO] EventProf enabled (sql.active_record)
........[TEST PROF INFO] EventProf results for sql.active_record

Total time: 00:04.958 of 00:09.912 (50.03%)
Total events: 3650

Top 5 slowest suites (by time):

EpicIssues::UpdateService (./ee/spec/services/epic_issues/update_service_spec.rb:5) – 00:04.958 (3650 / 8) of 00:09.912 (50.03%)



Finished in 12.89 seconds (files took 3.14 seconds to load)
8 examples, 0 failures

TEST PROF INFO - After

EVENT_PROF='sql.active_record' bin/rspec ./ee/spec/services/epic_issues/update_service_spec.rb
Running via Spring preloader in process 16088
[TEST PROF INFO] Activating EVENT_PROF with `Spring.after_fork`
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}
[TEST PROF INFO] EventProf enabled (sql.active_record)
........[TEST PROF INFO] EventProf results for sql.active_record

Total time: 00:01.518 of 00:03.781 (40.15%)
Total events: 858

Top 5 slowest suites (by time):

EpicIssues::UpdateService (./ee/spec/services/epic_issues/update_service_spec.rb:5) – 00:01.518 (858 / 8) of 00:03.781 (40.15%)



Finished in 6.73 seconds (files took 3.11 seconds to load)
8 examples, 0 failures

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