Add store labels to all Rails.cache metrics - 2nd attempt

What does this MR do and why?

This MR is a 2nd try of !121477 (merged). It has 4 main commits:

1. Revert of !121692 (merged) which effectively does !121477 (merged)
2. Adding spec which fails. Good news because now we have a test case to catch for invalid label set errors and any other obscure errors when running multiple subscriber methods in a transaction
3. The fix: a private method to increment gitlab_cache_misses_total so that we dont have to sync up all call-sites of .increment(:gitlab_cache_misses_total, ...)
4. Rubocop fix.

The root cause of the revert is that cache_generate and cache_read increments the counter gitlab_cache_misses_total but have different labels. There is a difference in label because only 1 of the 2 callsites added the new label. The respective specs were updated but does not account for when multiple metrics are incremented in a single webtransaction.

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Before	After

How to set up and validate locally

1. Checkout to the 2nd commit

git checkout 0beb2c0b45e9

2. Run the rspec

bundle exec rspec spec/lib/gitlab/metrics/subscribers/rails_cache_spec.rb

3. Observe 1 failed spec

Failures:

  1) Gitlab::Metrics::Subscribers::RailsCache when receiving multiple instrumentation hits in a transaction does not raises InvalidLabelSetError error
     Failure/Error:
       expect {
         subscriber.cache_read(event)
         subscriber.cache_read_multi(event)
         subscriber.cache_write(event)
         subscriber.cache_delete(event)
         subscriber.cache_exist?(event)
         subscriber.cache_fetch_hit(event)
         subscriber.cache_generate(event)
       }.not_to raise_error

       expected no Exception, got #<Prometheus::Client::LabelSetValidator::InvalidLabelSetError: labels must have the same signature: (... [:action, :controller, :feature_category], got: [:action, :controller, :feature_category, :store])> with backtrace:
         # ./lib/gitlab/metrics/transaction.rb:68:in `increment'
         # ./lib/gitlab/metrics/subscribers/rails_cache.rb:60:in `cache_generate'
         # ./spec/lib/gitlab/metrics/subscribers/rails_cache_spec.rb:27:in `block (4 levels) in <top (required)>'
         # ./spec/lib/gitlab/metrics/subscribers/rails_cache_spec.rb:20:in `block (3 levels) in <top (required)>'
         # ./spec/spec_helper.rb:424:in `block (3 levels) in <top (required)>'
         # ./spec/support/sidekiq_middleware.rb:18:in `with_sidekiq_server_middleware'
         # ./spec/spec_helper.rb:415:in `block (2 levels) in <top (required)>'
         # ./spec/spec_helper.rb:411:in `block (3 levels) in <top (required)>'
         # ./lib/gitlab/application_context.rb:61:in `with_raw_context'
         # ./spec/spec_helper.rb:411:in `block (2 levels) in <top (required)>'
         # ./spec/spec_helper.rb:242:in `block (2 levels) in <top (required)>'
         # ./spec/support/system_exit_detected.rb:7:in `block (2 levels) in <main>'
         # ./spec/support/database/prevent_cross_joins.rb:108:in `block (3 levels) in <main>'
         # ./spec/support/database/prevent_cross_joins.rb:62:in `with_cross_joins_prevented'
         # ./spec/support/database/prevent_cross_joins.rb:108:in `block (2 levels) in <main>'

4. Checkout to sc1-railscache-metric-granularity-2 and rerun the specs. There should be no failures this time.

MR acceptance checklist

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