[external metrics] fix configuration when registerAPIService is false

[celenechang]

What does this PR do?

When the External Metrics Server is set to not register an API Service, we were not creating other RBACs needed for the EMS. This PR fixes that issue.

Motivation

Bug fix

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

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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 30.76923% with 9 lines in your changes missing coverage. Please review.

Project coverage is 54.87%. Comparing base (7a522d3) to head (6f48203).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1255   +/-   ##
=======================================
  Coverage   54.87%   54.87%           
=======================================
  Files         241      241           
  Lines       27893    27893           
=======================================
  Hits        15305    15305           
  Misses      11717    11717           
  Partials      871      871           

Flag	Coverage Δ
unittests	54.87% <30.76%> (ø)

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Files	Coverage Δ
...rs/datadogagent/feature/externalmetrics/feature.go	41.88% <30.76%> (ø)

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