[MDS] Fix the dsm plugin setup when mds feature flag is disabled

[RyanL1997]

Description

Fix the dsm plugin setup when mds feature flag is disabled

Issues Resolved

• Resolve: [BUG] data_source.enabled: false causes getDataSourceMenu to fail #7154
• Relate: [MDS] Observability Datasource Plugin migration with MDS support #7143

#7143 introduced the behavior that Data source management plugin will always be registered, and this PR introduced the proper handling of DSM plugin setup when data_source.enabled is set to false.

Changelog

• fix: [MDS] Fix the dsm plugin setup when mds feature flag is disabled

Check List

• All tests pass
  • yarn test:jest
  • yarn test:jest_integration
• New functionality includes testing.
• New functionality has been documented.
• Update CHANGELOG.md
• Commits are signed per the DCO using --signoff

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.

Project coverage is 67.51%. Comparing base (daccab7) to head (c58b513).
Report is 1 commits behind head on main.

Files	Patch %	Lines
...rc/plugins/data_source_management/public/plugin.ts	72.72%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7163      +/-   ##
==========================================
+ Coverage   67.48%   67.51%   +0.02%     
==========================================
  Files        3468     3468              
  Lines       68375    68375              
  Branches    11114    11113       -1     
==========================================
+ Hits        46146    46162      +16     
+ Misses      19529    19516      -13     
+ Partials     2700     2697       -3     

Flag	Coverage Δ
Linux_1	33.05% <ø> (ø)
Linux_2	55.19% <ø> (ø)
Linux_3	45.35% <72.72%> (+0.01%)	⬆️
Linux_4	34.76% <0.00%> (ø)
Windows_1	33.09% <ø> (+0.02%)	⬆️
Windows_2	55.14% <ø> (ø)
Windows_3	45.37% <72.72%> (+0.01%)	⬆️
Windows_4	34.76% <0.00%> (ø)

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