Add specs to catch recursive feature-flag requests

What does this MR do and why?

This MR adds a spec to run Feature.enabled? through Rails.cache by adding use_clean_rails_redis_caching to the example. This catches usage of feature flags in any Redis instrumentation middleware or Gitlab::Redis::Cache/ActiveSupport::Cache::RedisStoreCache patches.

See #385237 (closed) for more background

Two complications when testing out the efficacy of this spec:

1. The line of code preventing it from being captured in gdk rails c has been fixed in MR.
2. The code causing the recursion has been reverted

This new spec was tested on a commit between its introduction and removal: https://gitlab.com/gitlab-org/gitlab/-/commits/sc1-investigate. The diff is fairly small, containing 1 line of code change and 5 lines of spec changes (same as this MR).

To test it, checkout to git checkout sc1-investigate and run the spec.

➜  gitlab git:(sc1-investigate) ✗ CI=true bundle exec rspec spec/lib/feature_spec.rb:165  -r spec_helper
/Users/sylvesterchin/work/gitlab-development-kit/gitlab/rspec/flaky/suite-report.json doesn't exist
Run options: include {:locations=>{"./spec/lib/feature_spec.rb"=>[165]}}
==> Starting GitLab Elasticsearch Indexer set up...
==> Starting Gitaly set up...

Test environment set up in 1.476678 seconds

1st Try error in ./spec/lib/feature_spec.rb:166:
(Feature).enabled?(:validate_allowed_cross_slot_commands, {:type=>:development})
    expected: 1 time with any arguments
    received: 2 times with arguments: (:validate_allowed_cross_slot_commands, {:type=>:development})

RSpec::Retry: 2nd try ./spec/lib/feature_spec.rb:166
F

Failures:

  1) Feature.enabled? when using redis cache does not make recursive feature-flag calls
     Failure/Error: Feature.enabled?(:validate_allowed_cross_slot_commands, type: :development)

       (Feature).enabled?(:validate_allowed_cross_slot_commands, {:type=>:development})
           expected: 1 time with any arguments
           received: 2 times with arguments: (:validate_allowed_cross_slot_commands, {:type=>:development})
     # ./lib/gitlab/instrumentation/redis_base.rb:82:in `block in validate_allowed_commands?'
     # ./lib/gitlab/null_request_store.rb:34:in `fetch'
     # ./lib/gitlab/safe_request_store.rb:12:in `fetch'
     # ./lib/gitlab/instrumentation/redis_base.rb:81:in `validate_allowed_commands?'
....
Finished in 3.06 seconds (files took 1 minute 0.4 seconds to load)
1 example, 1 failure

Failed examples:

rspec ./spec/lib/feature_spec.rb:166 # Feature.enabled? when using redis cache does not make recursive feature-flag calls

[TEST PROF INFO] Time spent in factories: 00:00.010 (0.03% of total time)

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How to set up and validate locally

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