refactor: simplify wehbook configuration controller handlers

[fabriziosestito]

Description

Before this change, we leveraged several annotations to check if a WebhookConfiguration was related to the type of policy managed by a controller.
For instance, the scope and group annotations were used to check if a policy was cluster or namespace scoped and if it was a group.
When adding PolicyGroups we realized that it was hard to maintain multiple annotations.

This PR simplifies the WebhookConfiguration controller handlers, by using just two annotations (name and namespace) and by using the client to check if the resource of a certain type exists.
This is ok regarding performance and API server load since the request is cached.
and returning a reconcile request.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.27%. Comparing base (141a393) to head (281414e).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #894      +/-   ##
==========================================
- Coverage   69.33%   69.27%   -0.06%     
==========================================
  Files          30       30              
  Lines        3052     3040      -12     
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- Hits         2116     2106      -10     
+ Misses        769      767       -2     
  Partials      167      167              

Flag	Coverage Δ
integration-tests	58.20% <100.00%> (-0.10%)	⬇️
unit-tests	40.41% <ø> (ø)

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[flavio]

Thanks an interesting approach. Are there consequences caused by using a field indexer?

[fabriziosestito]

Thanks an interesting approach. Are there consequences caused by using a field indexer?

I don't think so. However I'd like to proceed with the name, namespace approach for simplicty.