Speed up specs for EnvironmentStatus serializer

What does this MR do and why?

Use let_it_be + before_all to reduce SQL queries.

This spec can be run in random order.

Contributes to &8745.

RSpec Profiling

Here's the output from test-prof when run with FPROF=1. Note:

• Total amount of factories created went down from 161 to 12 🚀
• Total events went down from 5101 to 660
• Queries saved: 4441

Before

[TEST PROF INFO] Time spent in factories: 00:24.034 (69.33% of total time)
[TEST PROF INFO] Factories usage

 Total: 161
 Total top-level: 49
 Total time: 00:24.034 (out of 00:38.689)
 Total uniq factories: 9

   total   top-level     total time      time per call      top-level time               name

      32           0       18.1921s            0.5685s             0.0000s            project
      32           0        3.3282s            0.1040s             0.0000s          namespace
      16          16       11.3230s            0.7077s            11.3230s         deployment
      16           0        9.7281s            0.6080s             0.0000s        environment
      16           0        0.3727s            0.0233s             0.0000s        ci_pipeline
      16           0        0.7212s            0.0451s             0.0000s           ci_build
      16          16       11.4436s            0.7152s            11.4436s      merge_request
      16          16        1.2524s            0.0783s             1.2524s               user
       1           1        0.0156s            0.0156s             0.0156s            license

After

[TEST PROF INFO] Time spent in factories: 00:02.621 (20.01% of total time)
[TEST PROF INFO] Factories usage

 Total: 12
 Total top-level: 5
 Total time: 00:02.621 (out of 00:17.008)
 Total uniq factories: 9

   total   top-level     total time      time per call      top-level time               name

       2           2        0.5891s            0.2946s             0.5891s               user
       2           0        1.4486s            0.7243s             0.0000s            project
       2           0        0.1742s            0.0871s             0.0000s          namespace
       1           1        0.0123s            0.0123s             0.0123s            license
       1           1        1.2511s            1.2511s             1.2511s         deployment
       1           0        1.0112s            1.0112s             0.0000s        environment
       1           0        0.0733s            0.0733s             0.0000s        ci_pipeline
       1           0        0.1167s            0.1167s             0.0000s           ci_build
       1           1        0.7689s            0.7689s             0.7689s      merge_request

How to set up and validate locally

bin/rspec ./spec/serializers/environment_status_entity_spec.rb

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.