add generation changed predicate to dda controller

[celenechang]

What does this PR do?

Add GenerationChanged predicate to DatadogAgent controller to prevent Status updates from triggering reconciles on the resource.

Motivation

Before change (two reconcilers per period):

{"level":"INFO","ts":"2024-10-25T11:41:39.377Z","logger":"controllers.DatadogAgent","msg":"Reconciling DatadogAgent","datadogagent":{"name":"datadog","namespace":"system"}}
{"level":"INFO","ts":"2024-10-25T11:41:39.743Z","logger":"controllers.DatadogAgent","msg":"Reconciling DatadogAgent","datadogagent":{"name":"datadog","namespace":"system"}}
{"level":"INFO","ts":"2024-10-25T11:41:54.377Z","logger":"controllers.DatadogAgent","msg":"Reconciling DatadogAgent","datadogagent":{"name":"datadog","namespace":"system"}}
{"level":"INFO","ts":"2024-10-25T11:41:54.743Z","logger":"controllers.DatadogAgent","msg":"Reconciling DatadogAgent","datadogagent":{"name":"datadog","namespace":"system"}}
{"level":"INFO","ts":"2024-10-25T11:42:09.743Z","logger":"controllers.DatadogAgent","msg":"Reconciling DatadogAgent","datadogagent":{"name":"datadog","namespace":"system"}}
{"level":"INFO","ts":"2024-10-25T11:42:09.864Z","logger":"controllers.DatadogAgent","msg":"Reconciling DatadogAgent","datadogagent":{"name":"datadog","namespace":"system"}}

After (1 reconcile per period):

{"level":"INFO","ts":"2024-10-25T11:51:46.344Z","logger":"controllers.DatadogAgent","msg":"Reconciling DatadogAgent","datadogagent":{"name":"datadog","namespace":"system"}}
{"level":"INFO","ts":"2024-10-25T11:52:01.465Z","logger":"controllers.DatadogAgent","msg":"Reconciling DatadogAgent","datadogagent":{"name":"datadog","namespace":"system"}}
{"level":"INFO","ts":"2024-10-25T11:52:16.553Z","logger":"controllers.DatadogAgent","msg":"Reconciling DatadogAgent","datadogagent":{"name":"datadog","namespace":"system"}}

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

• Deploy the latest Datadog Operator and apply a DatadogAgent manifest

• View the logs to see reconcile frequency (Reconciling DatadogAgent). It is expected to be at least twice per second, every 15s.

• Deploy the test image

• Check the reconcile frequency. The number of reconciles should be reduced (in my test environment, it went down to once every 15s).

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

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 48.70%. Comparing base (734366f) to head (9472213).

Files with missing lines	Patch %	Lines
internal/controller/datadogagent_controller.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1486      +/-   ##
==========================================
- Coverage   48.72%   48.70%   -0.02%     
==========================================
  Files         224      224              
  Lines       19845    19845              
==========================================
- Hits         9669     9666       -3     
- Misses       9668     9670       +2     
- Partials      508      509       +1     

Flag	Coverage Δ
unittests	48.70% <0.00%> (-0.02%)	⬇️

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

Files with missing lines	Coverage Δ
internal/controller/datadogagent_controller.go	66.97% <0.00%> (-2.76%)	⬇️

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