Support API Key for authentication

[EngHabu]

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- Use #patch, #minor or #major in the pull-request title to bump the corresponding version. Otherwise, the patch version will be bumped. More details

TL;DR

Please replace this text with a description of what this PR accomplishes.

Type

• [ ] Bug Fix
• [ ] Feature
• [ ] Plugin

Are all requirements met?

• [ ] Code completed
• [ ] Smoke tested
• [ ] Unit tests added
• [ ] Code documentation added
• [ ] Any pending items have an associated Issue

Complete description

How did you fix the bug, make the feature etc. Link to any design docs etc

Tracking Issue

Remove the 'fixes' keyword if there will be multiple PRs to fix the linked issue

fixes https://github.com/flyteorg/flyte/issues/

Follow-up issue

NA OR https://github.com/flyteorg/flyte/issues/

[codecov[bot]]

Codecov Report

Merging #384 (f2d7fd4) into master (bdb7630) will increase coverage by 1.27%. Report is 25 commits behind head on master. The diff coverage is 56.66%.

:exclamation: Current head f2d7fd4 differs from pull request most recent head 71406e7. Consider uploading reports for the commit 71406e7 to get more accurate results

@@            Coverage Diff             @@
##           master     #384      +/-   ##
==========================================
+ Coverage   76.71%   77.99%   +1.27%     
==========================================
  Files          18       19       +1     
  Lines        1426     1268     -158     
==========================================
- Hits         1094      989     -105     
+ Misses        280      224      -56     
- Partials       52       55       +3     

Flag	Coverage Δ
unittests	?

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Files Changed	Coverage Δ
clients/go/admin/config.go	50.00% <ø> (ø)
clients/go/admin/token_source_provider.go	56.41% <47.82%> (-2.42%)	:arrow_down:
clients/go/admin/api_key.go	85.71% <85.71%> (ø)

... and 16 files with indirect coverage changes