[kubectl plugin] Fallback to configmap leader attempt for clusteragent if lease failed

[tbavelier]

What does this PR do?

Falls back to try getting leader from configmap for clusteragent even if leases are supported, in the case getting leader from lease failed

Motivation

Allows to get leader from configmap even if leases are supported in the environment, in a situation where configmap is still being used for leader election of DCA

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

• As fix: support lease obj in kubectl datadog clusteragent leader cmd #1375, check by default, we try to retrieve leader when leader_election_default_resource is set to lease
• In an env with DCA leader election in configmap (https://github.com/DataDog/datadog-agent/blob/5e42ef8869290dcdec42772b0b71538485879f8b/pkg/config/setup/config.go#L515) but leases supported in the cluster, ensure you get the DCA leader

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

❌ Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.79%. Comparing base (b93f515) to head (86062da).
⚠️ Report is 153 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/kubectl-datadog/clusteragent/leader/leader.go	0.00%	9 Missing ⚠️

❌ Your patch status has failed because the patch coverage (0.00%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1833      +/-   ##
==========================================
- Coverage   49.80%   49.79%   -0.01%     
==========================================
  Files         221      221              
  Lines       21451    21452       +1     
==========================================
  Hits        10683    10683              
- Misses      10221    10222       +1     
  Partials      547      547              

Flag	Coverage Δ
unittests	49.79% <0.00%> (-0.01%)	⬇️

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

Files with missing lines	Coverage Δ
cmd/kubectl-datadog/clusteragent/leader/leader.go	0.00% <0.00%> (ø)

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b93f515...86062da. Read the comment docs.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[clamoriniere]

for now we don't make a difference between lease not found or RBAC issue.
maybe a jira card can be created to track this improvement, but IMO not needed now.

thanks for the fix 🙇