feat: Consumer Groups can be configured in Consumer

[programmer04]

What this PR does / why we need it:

Introduce the optional field ConsumerGroups to KongConsumer CRD that allows configuring Consumer Groups for Consumer. Add implementation and enhance integration test to cover it.

Which issue this PR fixes:

part of #3728

Special notes for your reviewer:

Integration test TestConsumerGroup is executed for two set-ups:

• DBMode (Postgres) - it passes without problems 🟢
• DBLess - it doesn't pass due to a bug in Kong Gateway reported by me to them in FTI-5264 (thus the status of this PR is blocked) 🔴 so test is skipped for such configuration for now

The golden test has been introduced for consumer groups with consumers.

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

Patch coverage: 7.6% and project coverage change: -5.8% ⚠️

Comparison is base (1d7296b) 67.5% compared to head (631da10) 61.7%.

❗ Current head 631da10 differs from pull request most recent head 75d72d4. Consider uploading reports for the commit 75d72d4 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4419     +/-   ##
=======================================
- Coverage   67.5%   61.7%   -5.8%     
=======================================
  Files        159     159             
  Lines      18772   18762     -10     
=======================================
- Hits       12681   11588   -1093     
- Misses      5327    6502   +1175     
+ Partials     764     672     -92     

Files Changed	Coverage Δ
internal/dataplane/deckgen/generate.go	43.5% <0.0%> (-14.7%)	⬇️
internal/dataplane/kongstate/consumer.go	100.0% <ø> (ø)
internal/dataplane/kongstate/kongstate.go	64.5% <11.1%> (-7.1%)	⬇️

... and 33 files with indirect coverage changes

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[rainest]

Code looks fine on our end. Some copyediting comments.

We may want to dispense with the integration test (especially since it's broken for reasons beyond our control) and only do unit or golden tests for the consumer+group assignment. Ultimately (once plugin assignment is complete) we should end up with a single test that confirms proper mapping by assigning a plugin to the consumer group and confirming that it runs.

Querying the admin API to confirm the objects is atypical.(I thought it odd there was a special workspaced client if case, and then realized that no other integration test has this because this is the only one that checks the admin API. KIC integration tests generally observe the effects of their configuration instead of the config itself, since the effect implies the presence of the configuration.

[programmer04]

In terms of testing @rainest I consider this state as intermediate as I've written in PR that introduces this test #4387

The introduced integration test TestConsumerGroup will evolve in the future to cover all features of it e.g. adding Consumers to Consumer Group. Since Consumer Group doesn't do anything useful yet for now check directly in Gateway if it was created. Later it will be replaced with a proper testing scenario.

So it's a pretty low cost to have it like that for now and later when the full feature will be implemented adjust it. It allowed me to discover problems during development like the broken Kong Gateway.

I've introduced a golden test too.