[datadog-monitor] Init fake client store with test objects instead of using create

[tbavelier]

What does this PR do?

Proposes a way to re-enable the finalizer removal test by initialising the object store with objects in the desired state, mimicking the k8s lifecycle:

1. Custom resource gets created
2. Operator adds finalizer
3. Custom resource is scheduled for deletion (e.g. user ran kubectl delete)
4. A deletion timestamp is added but the resource is not yet deleted since it has a finalizer
5. Operator cleans the finalizer
6. As the object has a deletion timestamp and no finalizer, it gets deleted

Motivation

#1175 upgraded the controller runtime to a version above 0.15.x which prevents objects from being created with a deletion timestamp (or updated/patched), preventing us to test the finalizer removal. So it was disabled in the meantime.

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

Write there any instructions and details you may have to test your PR.

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

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.66%. Comparing base (756ed08) to head (3c039e9).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1538   +/-   ##
=======================================
  Coverage   48.66%   48.66%           
=======================================
  Files         226      226           
  Lines       20370    20370           
=======================================
  Hits         9913     9913           
  Misses       9940     9940           
  Partials      517      517           

Flag	Coverage Δ
unittests	48.66% <ø> (ø)

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