Make it possible to configure flyte with an externally managed Secret

[mhotan]

• Make adminOauthClientCredentials secret name configurable.
• This makes it possible to manage the Kubernetes secret outside the flyte-core helm chart.

Tracking issue

N/A

Why are the changes needed?

Union manages flyte-core helm release via ArgoCD. We identified that managing the oath client secret was appropriate outside of the flyte-core helm release and, thus, outside of a Git repository watched by ArgoCD. This situation will likely surface for other flyte users. We are thus backporting these changes from Union to Flyte OSS.

How was this patch tested?

This change was tested and release to all Union managed data planes.

Setup process

Screenshots

Check all the applicable boxes

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

Related PRs

Docs link

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 36.17%. Comparing base (5c147ef) to head (9b7a65c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5700   +/-   ##
=======================================
  Coverage   36.17%   36.17%           
=======================================
  Files        1302     1302           
  Lines      109614   109614           
=======================================
  Hits        39653    39653           
  Misses      65816    65816           
  Partials     4145     4145           

Flag	Coverage Δ
unittests-datacatalog	51.37% <ø> (ø)
unittests-flyteadmin	55.30% <ø> (ø)
unittests-flytecopilot	12.17% <ø> (ø)
unittests-flytectl	62.18% <ø> (ø)
unittests-flyteidl	7.12% <ø> (ø)
unittests-flyteplugins	53.34% <ø> (ø)
unittests-flytepropeller	41.71% <ø> (ø)
unittests-flytestdlib	55.33% <ø> (ø)

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