Several informer related changes

[shawkins]

Description

This addresses a host of informer related requests:

Fix #3969 - stop emitting sync events on relist - it was simplest to make this change to support #3968
Fix #3968 - added SharedInformer.initialState to set

Also took the parts of #3943 that were most general purpose, such as being able to add/remove indexers at any time, along with deprecating Informable.withIndexers

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change
• Chore (non-breaking change which doesn't affect codebase;
  test, version modification, documentation, etc.)

Checklist

• Code contributed by me aligns with current project license: Apache 2.0
• I Added CHANGELOG entry regarding this change
• I have implemented unit tests to cover my changes
• I have added/updated the javadocs and other documentation accordingly
• No new bugs, code smells, etc. in SonarCloud report
• I tested my code in Kubernetes
• I tested my code in OpenShift

[sonarcloud]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
3 Code Smells

50.0% Coverage
0.0% Duplication