feat(databricks): support override Databricks instances

[pingsutw]

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• I updated the documentation accordingly.
• All new and existing tests passed.
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[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 37.53%. Comparing base (2f38d65) to head (9c66353).
Report is 108 commits behind head on master.

Files	Patch %	Lines
...ugins/go/tasks/plugins/webapi/databricks/plugin.go	88.88%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #5358       +/-   ##
===========================================
- Coverage   61.09%   37.53%   -23.56%     
===========================================
  Files         794     1301      +507     
  Lines       51213   112713    +61500     
===========================================
+ Hits        31288    42306    +11018     
- Misses      17044    66234    +49190     
- Partials     2881     4173     +1292     

Flag	Coverage Δ
unittests-datacatalog	51.37% <ø> (-17.95%)	⬇️
unittests-flyteadmin	55.56% <ø> (-3.31%)	⬇️
unittests-flytecopilot	12.17% <ø> (-5.62%)	⬇️
unittests-flytectl	65.68% <ø> (-2.62%)	⬇️
unittests-flyteidl	7.32% <ø> (-71.98%)	⬇️
unittests-flyteplugins	54.94% <88.88%> (-7.01%)	⬇️
unittests-flytepropeller	42.91% <ø> (-14.41%)	⬇️
unittests-flytestdlib	55.79% <ø> (-9.94%)	⬇️

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