fix: do not require namespaces when parsing errors about cluster scoped resources

[pmalek]

What this PR does / why we need it:

This PR will fix an error when user does not have the admission webhook enabled and applies a configuration which has a cluster scoped resource being the offender, e.g. KongClusterPlugin with incorrect schema which up until now yields:

2024-02-04T18:19:55Z    error    Entity tags missing fields    {"name": "prometheus", "error": "no namespace"}

Since KongClusterPlugin is cluster scoped it does not have a namespace. This PR fixes that.

Fixes: #5555

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 73.4%. Comparing base (713765d) to head (e63c663).

Files	Patch %	Lines
...al/dataplane/sendconfig/inmemory_error_handling.go	60.0%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #5764   +/-   ##
=====================================
  Coverage   73.4%   73.4%           
=====================================
  Files        175     175           
  Lines      18147   18151    +4     
=====================================
+ Hits       13321   13335   +14     
+ Misses      3856    3844   -12     
- Partials     970     972    +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.