Add flightrecorder feature to the operator

[misteriaud]

Summary

• Adds spec.features.flightRecorder.enabled to the DatadogAgent CRD
• Creates a flightrecorder sidecar container in the agent pod when enabled
• Sets up shared Unix socket volume (/var/run/flightrecorder) for agent-to-flightrecorder IPC
• Sets up data volume (/data/signals) for Vortex columnar output files
• Configures DD_FLIGHTRECORDER_ENABLED and DD_FLIGHTRECORDER_SOCKET_PATH env vars on the core agent

Test plan

• Unit tests for feature enable/disable and volume/env var configuration
• go build ./... passes
• go test ./internal/controller/datadogagent/feature/... passes
• Verified in local kind cluster: flightrecorder container starts, listens on socket, volumes mounted correctly

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 54.54545% with 50 lines in your changes missing coverage. Please review.
✅ Project coverage is 39.04%. Comparing base (40e907c) to head (561f8b5).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...controller/datadogagent/component/agent/default.go	0.00%	29 Missing ⚠️
...ler/datadogagent/feature/flightrecorder/feature.go	83.09%	10 Missing and 2 partials ⚠️
pkg/testutils/builder.go	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2785      +/-   ##
==========================================
+ Coverage   38.78%   39.04%   +0.26%     
==========================================
  Files         309      310       +1     
  Lines       26839    27080     +241     
==========================================
+ Hits        10409    10573     +164     
- Misses      15650    15719      +69     
- Partials      780      788       +8     

Flag	Coverage Δ
unittests	39.04% <54.54%> (+0.26%)	⬆️

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	92.85% <ø> (ø)
...ontroller/datadogagent/override/podtemplatespec.go	77.70% <100.00%> (+0.15%)	⬆️
pkg/testutils/builder.go	0.00% <0.00%> (ø)
...ler/datadogagent/feature/flightrecorder/feature.go	83.09% <83.09%> (ø)
...controller/datadogagent/component/agent/default.go	42.89% <0.00%> (-1.79%)	⬇️

... and 4 files with indirect coverage changes

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