[Backport 2.x] [Saved Object Service] Adds Repository Factory Provider

[opensearch-trigger-bot]

Backport 5c5de03 from #4149.

[codecov]

Codecov Report

Merging #4244 (bb3e682) into 2.x (8af035d) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              2.x    #4244      +/-   ##
==========================================
+ Coverage   66.36%   66.38%   +0.01%     
==========================================
  Files        3229     3229              
  Lines       62114    62121       +7     
  Branches     9616     9619       +3     
==========================================
+ Hits        41224    41241      +17     
+ Misses      18571    18560      -11     
- Partials     2319     2320       +1     

Flag	Coverage Δ
Linux	66.31% <100.00%> (+<0.01%)	⬆️
Windows	66.33% <100.00%> (+0.02%)	⬆️

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Impacted Files	Coverage Δ
src/core/server/legacy/legacy_service.ts	75.38% <ø> (ø)
src/core/server/plugins/plugin_context.ts	45.45% <ø> (ø)
...server/saved_objects/saved_objects_service.mock.ts	100.00% <ø> (ø)
...aved_objects/service/lib/scoped_client_provider.ts	100.00% <ø> (ø)
...core/server/saved_objects/saved_objects_service.ts	85.71% <100.00%> (+1.58%)	⬆️

... and 2 files with indirect coverage changes