[CECO-1860][DatadogGenericResource] Refactor handler

[tbavelier]

What does this PR do?

• Slightly refactors GenericResource controller to use interfaces avoiding code duplication and improving readability+maintenance
• Some additional small fixes:
  • move id conversion functions to utils.go from notebooks.go
  • move synthetics status update function to synthetics.go from utils.go (and associated test)
  • follow-up to 7b2552eff907c205bf8ce968ac040030fe0d3da3[: moving away from specific notebook id conversion to generic](b198577)
  • nit: fix update error message

Motivation

What inspired you to submit this pull request?

Additional Notes

Anything else we should know when reviewing?

Minimum Agent Versions

Are there minimum versions of the Datadog Agent and/or Cluster Agent required?

• Agent: vX.Y.Z
• Cluster Agent: vX.Y.Z

Describe your test plan

Same instructions as #1534, can use config/samples/datadoghq_v1alpha1_datadoggenericresource.yaml

Checklist

• PR has at least one valid label: bug, enhancement, refactoring, documentation, tooling, and/or dependencies
• PR has a milestone or the qa/skip-qa label

[tbavelier]

This is necessary as the switch case for deletion handler now panics on unsupported/empty resource type

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 55.31915% with 63 lines in your changes missing coverage. Please review.

Project coverage is 48.96%. Comparing base (98ae1c6) to head (049c0b0).

Files with missing lines	Patch %	Lines
...al/controller/datadoggenericresource/synthetics.go	52.11%	34 Missing ⚠️
...nal/controller/datadoggenericresource/notebooks.go	10.71%	25 Missing ⚠️
...nternal/controller/datadoggenericresource/utils.go	90.47%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1634      +/-   ##
==========================================
+ Coverage   48.93%   48.96%   +0.02%     
==========================================
  Files         217      217              
  Lines       20892    20880      -12     
==========================================
  Hits        10223    10223              
+ Misses      10129    10117      -12     
  Partials      540      540              

Flag	Coverage Δ
unittests	48.96% <55.31%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...nternal/controller/datadoggenericresource/utils.go	92.98% <90.47%> (+35.93%)	⬆️
...nal/controller/datadoggenericresource/notebooks.go	11.11% <10.71%> (-5.92%)	⬇️
...al/controller/datadoggenericresource/synthetics.go	31.09% <52.11%> (+31.09%)	⬆️

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