DB testing: Artifact full query log for each migration

What does this MR do?

Artifact the query log for each migration that is run in the DB testing pipeline. All files placed in tmp/migration-testing/ are saved as pipeline artifacts (https://gitlab.com/gitlab-org/database-team/gitlab-com-database-testing/-/blob/master/.gitlab-ci.yml#L65).

Related to gitlab-org/database-team/team-tasks#144 (closed)

Screenshots (strongly suggested)

Test pipeline: !60020 (comment 558179849)

Sample log file: 20210422152437.log

D, [2021-05-10T20:28:02.782467 #30] DEBUG -- :   [1m[35m (37.2ms)[0m  [1m[34mSELECT pg_try_advisory_lock(3005434223539248480)[0m
D, [2021-05-10T20:28:02.783087 #30] DEBUG -- :   ↳ lib/tasks/gitlab/db.rake:240:in `block (5 levels) in <main>'
D, [2021-05-10T20:28:02.857533 #30] DEBUG -- :   [1m[35m (73.6ms)[0m  [1m[34mSELECT "schema_migrations"."version" FROM "schema_migrations" ORDER BY "schema_migrations"."version" ASC /*application:test*/[0m
D, [2021-05-10T20:28:02.858060 #30] DEBUG -- :   ↳ lib/tasks/gitlab/db.rake:240:in `block (5 levels) in <main>'
I, [2021-05-10T20:28:02.866516 #30]  INFO -- : Migrating to TestMigration (20210422152437)
D, [2021-05-10T20:28:02.905645 #30] DEBUG -- :   [1m[35m (37.1ms)[0m  [1m[35mBEGIN /*application:test*/[0m
D, [2021-05-10T20:28:02.906594 #30] DEBUG -- :   ↳ lib/gitlab/database.rb:360:in `block in transaction'
D, [2021-05-10T20:28:02.949813 #30] DEBUG -- :   [1m[35m (42.9ms)[0m  [1m[35mALTER TABLE "user_statuses" ADD "test_column" integer /*application:test*/[0m
D, [2021-05-10T20:28:02.950591 #30] DEBUG -- :   ↳ lib/gitlab/database.rb:360:in `block in transaction'
D, [2021-05-10T20:28:02.988987 #30] DEBUG -- :   [1m[36mprimary::SchemaMigration Create (37.0ms)[0m  [1m[32mINSERT INTO "schema_migrations" ("version") VALUES ('20210422152437') RETURNING "version" /*application:test*/[0m
D, [2021-05-10T20:28:02.990018 #30] DEBUG -- :   ↳ lib/gitlab/database.rb:360:in `block in transaction'
D, [2021-05-10T20:28:03.027956 #30] DEBUG -- :   [1m[35m (37.3ms)[0m  [1m[35mCOMMIT /*application:test*/[0m
D, [2021-05-10T20:28:03.028709 #30] DEBUG -- :   ↳ lib/gitlab/database.rb:360:in `block in transaction'
D, [2021-05-10T20:28:03.067224 #30] DEBUG -- :   [1m[36mActiveRecord::InternalMetadata Load (37.4ms)[0m  [1m[34mSELECT "ar_internal_metadata".* FROM "ar_internal_metadata" WHERE "ar_internal_metadata"."key" = 'environment' LIMIT 1 /*application:test*/[0m
D, [2021-05-10T20:28:03.067898 #30] DEBUG -- :   ↳ lib/tasks/gitlab/db.rake:240:in `block (5 levels) in <main>'
D, [2021-05-10T20:28:03.106513 #30] DEBUG -- :   [1m[35m (37.3ms)[0m  [1m[34mSELECT pg_advisory_unlock(3005434223539248480)[0m
D, [2021-05-10T20:28:03.106944 #30] DEBUG -- :   ↳ lib/tasks/gitlab/db.rake:240:in `block (5 levels) in <main>'
D, [2021-05-10T20:28:03.231510 #30] DEBUG -- :   [1m[35m (124.2ms)[0m  [1m[34mselect pg_database_size(current_database()) /*application:test*/[0m
D, [2021-05-10T20:28:03.232102 #30] DEBUG -- :   ↳ lib/gitlab/database/migrations/observers/total_database_size_change.rb:25:in `get_total_database_size'

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