fix: deck content to dbless converter

[programmer04]

What this PR does / why we need it:

• Configuration for which IDs are filled, but names are not is invalid, so the converter should not panic
• Use plugins[].consumer_group (new method of working with consumer groups and plugins for Gateway >= 3.4) instead of consumer_group_plugins (obsolete - used by old implementation of consumer groups Gateway < 3.4, used by mistake in the first implementation), otherwise Gateway rejects config

Which issue this PR fixes:

Continuation of #4453

[codecov]

Codecov Report

Patch coverage: 100.0% and project coverage change: -0.1% ⚠️

Comparison is base (9dfe212) 67.7% compared to head (011aabb) 67.6%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4459     +/-   ##
=======================================
- Coverage   67.7%   67.6%   -0.1%     
=======================================
  Files        161     161             
  Lines      18840   18832      -8     
=======================================
- Hits       12758   12746     -12     
- Misses      5319    5325      +6     
+ Partials     763     761      -2     

Files Changed	Coverage Δ
internal/dataplane/kongstate/kongstate.go	72.3% <ø> (ø)
internal/dataplane/sendconfig/inmemory_schema.go	100.0% <100.0%> (ø)

... and 5 files with indirect coverage changes

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[pmalek]

What is the base of this change, that is is it mentioned somewhere in spec or docs? 🤔

[programmer04]

In the source code that I referred to in the description (I enhanced it) @pmalek. In the first implementation #4453, @czeslavo was misguided. I discovered it during work on #4452, we looked into the Gateway source and proposed this PR. Unfortunately, Kong Gateway doesn't have proper documentation for dbless declarative config format