Add experiment signals to fleet remote config

[khewonc]

What does this PR do?

Adds experiment signals: start, stop, and promote. This depends on #2838. The latest commit contains the relevant changes

Motivation

https://datadoghq.atlassian.net/browse/CONTP-1424
https://datadoghq.atlassian.net/browse/CONTP-1425
https://datadoghq.atlassian.net/browse/CONTP-1426

Additional Notes

Merge after #2838

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

TBD

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)

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Reviewed commit: 2e153f00f4

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 74.46237% with 95 lines in your changes missing coverage. Please review.
✅ Project coverage is 40.50%. Comparing base (a646370) to head (eb7b351).

Files with missing lines	Patch %	Lines
pkg/fleet/daemon.go	69.70%	58 Missing and 15 partials ⚠️
internal/controller/datadogagent/revision.go	79.41%	4 Missing and 3 partials ⚠️
internal/controller/datadogagent/experiment.go	86.11%	3 Missing and 2 partials ⚠️
pkg/remoteconfig/updater.go	0.00%	4 Missing ⚠️
cmd/main.go	0.00%	3 Missing ⚠️
pkg/fleet/experiment.go	93.18%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2872      +/-   ##
==========================================
+ Coverage   40.03%   40.50%   +0.47%     
==========================================
  Files         319      320       +1     
  Lines       28066    28378     +312     
==========================================
+ Hits        11235    11495     +260     
- Misses      16008    16041      +33     
- Partials      823      842      +19     

Flag	Coverage Δ
unittests	40.50% <74.46%> (+0.47%)	⬆️

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

Files with missing lines	Coverage Δ
pkg/fleet/remote_config.go	100.00% <100.00%> (ø)
cmd/main.go	6.66% <0.00%> (ø)
pkg/fleet/experiment.go	93.18% <93.18%> (ø)
pkg/remoteconfig/updater.go	0.00% <0.00%> (ø)
internal/controller/datadogagent/experiment.go	86.17% <86.11%> (+1.39%)	⬆️
internal/controller/datadogagent/revision.go	78.12% <79.41%> (-3.39%)	⬇️
pkg/fleet/daemon.go	65.93% <69.70%> (+65.93%)	⬆️

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[datadog-prod-us1-6]

❌ Code Coverage

✨ Fix all issues with BitsAI

🛑 Gate Violations

🎯 1 Code Coverage issue detected

A Patch coverage percentage gate may be blocking this PR.

• Patch coverage: 73.33% (threshold: 80.00%)

ℹ️ Info

🎯 Code Coverage (details)
• Patch Coverage: 73.33%
• Overall Coverage: 40.58% (+0.47%)

_{This comment will be updated automatically if new data arrives.
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