[flyteagent] Enable agent-service in every configuration

[Future-Outlier]

Tracking issue

#3936

Why are the changes needed?

I found that gke-starter.yaml doesn't enable agent-service in it's helm chart, since agent watcher is merged and well-tested, we can enable agent-service whether agent is deployed or not.

What changes were proposed in this pull request?

add agent-service in every config that has enabled-plugins section.

How was this patch tested?

cd docker/sandbox-bundled
make build
flytectl demo start --force --disable-agent --image flyte-sandbox:latest

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

I will update the documentation in the follow-up PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 36.21%. Comparing base (a058fd1) to head (964d333).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5730      +/-   ##
==========================================
- Coverage   36.21%   36.21%   -0.01%     
==========================================
  Files        1303     1303              
  Lines      109560   109560              
==========================================
- Hits        39675    39674       -1     
- Misses      65765    65766       +1     
  Partials     4120     4120              

Flag	Coverage Δ
unittests-datacatalog	51.37% <ø> (ø)
unittests-flyteadmin	55.63% <ø> (ø)
unittests-flytecopilot	12.17% <ø> (ø)
unittests-flytectl	62.17% <ø> (ø)
unittests-flyteidl	7.12% <ø> (ø)
unittests-flyteplugins	53.35% <ø> (ø)
unittests-flytepropeller	41.76% <ø> (ø)
unittests-flytestdlib	55.33% <ø> (-0.03%)	⬇️

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