(No-op) SA1019: Remove deprecated functions usage

[tbavelier]

What does this PR do?

• Replaces all deprecated functions with the modern equivalent

Motivation

• Same as (No-op) Remove duplicate imports #2420 : Reduce number of staticcheck linter (disabled for now) violations

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

Tested the plugin manually, verified metrics forwarder is still working and is stopped on object removal

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

❌ Patch coverage is 0% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 38.06%. Comparing base (13a04a6) to head (bf37b32).

Files with missing lines	Patch %	Lines
cmd/kubectl-datadog/flare/flare.go	0.00%	10 Missing ⚠️
cmd/kubectl-datadog/agent/check/check.go	0.00%	5 Missing ⚠️
pkg/controller/utils/datadog/metrics_forwarder.go	0.00%	3 Missing ⚠️
cmd/check-operator/upgrade/upgrade.go	0.00%	2 Missing ⚠️
cmd/helpers/secrets/secrets.go	0.00%	2 Missing ⚠️
hack/generate-docs/generate-docs.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2478      +/-   ##
==========================================
- Coverage   38.06%   38.06%   -0.01%     
==========================================
  Files         290      290              
  Lines       24760    24763       +3     
==========================================
  Hits         9425     9425              
- Misses      14620    14623       +3     
  Partials      715      715              

Flag	Coverage Δ
unittests	38.06% <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
hack/generate-docs/generate-docs.go	0.00% <0.00%> (ø)
cmd/check-operator/upgrade/upgrade.go	0.00% <0.00%> (ø)
cmd/helpers/secrets/secrets.go	0.00% <0.00%> (ø)
pkg/controller/utils/datadog/metrics_forwarder.go	31.90% <0.00%> (-0.07%)	⬇️
cmd/kubectl-datadog/agent/check/check.go	9.60% <0.00%> (-0.06%)	⬇️
cmd/kubectl-datadog/flare/flare.go	0.00% <0.00%> (ø)

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