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 lines in your changes are missing coverage. Please review.

Project coverage is 61.10%. Comparing base (2f38d65) to head (9c66353).

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%   61.10%   +0.01%     
==========================================
  Files         794      794              
  Lines       51213    51216       +3     
==========================================
+ Hits        31288    31298      +10     
+ Misses      17044    17037       -7     
  Partials     2881     2881              

Flag	Coverage Δ
unittests-datacatalog	69.31% <ø> (ø)
unittests-flyteadmin	58.90% <ø> (+0.04%)	⬆️
unittests-flytecopilot	17.79% <ø> (ø)
unittests-flytectl	68.30% <ø> (ø)
unittests-flyteidl	79.30% <ø> (ø)
unittests-flyteplugins	61.96% <88.88%> (+0.01%)	⬆️
unittests-flytepropeller	57.32% <ø> (ø)
unittests-flytestdlib	65.75% <ø> (+0.02%)	⬆️

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