[CONTP-1587] DatadogGenericResource docs: soft deprecate other controllers and graduate out of preview

[tbavelier]

What does this PR do?

• Adds soft depreciation notices to DatadogSLO, DatadogMonitor, DatadogDashboard documentation pages
• Recommends using DDGR instead
• Provide "migration" document

Sister documentation PR: DataDog/documentation#37588

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

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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
• All commits are signed (see: signing commits)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.96%. Comparing base (3748b72) to head (f2f449c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3152   +/-   ##
=======================================
  Coverage   43.96%   43.96%           
=======================================
  Files         377      377           
  Lines       30774    30774           
=======================================
  Hits        13530    13530           
  Misses      16327    16327           
  Partials      917      917           

Flag	Coverage Δ
unittests	43.96% <ø> (ø)

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