[Backport 2.x] Datasource id is required if multiple datasource is enabled and no default cluster supported

[opensearch-trigger-bot]

Backport bbd40e1 from #5751.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (040a7f0) 66.94% compared to head (ee6aa79) 66.99%.

Files	Patch %	Lines
...a/server/search/opensearch_search/decide_client.ts	66.66%	0 Missing and 1 partial ⚠️
...ch/opensearch_search/opensearch_search_strategy.ts	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              2.x    #5842      +/-   ##
==========================================
+ Coverage   66.94%   66.99%   +0.05%     
==========================================
  Files        3300     3300              
  Lines       63545    63548       +3     
  Branches    10131    10134       +3     
==========================================
+ Hits        42539    42577      +38     
+ Misses      18546    18515      -31     
+ Partials     2460     2456       -4     

Flag	Coverage Δ
Linux_1	35.23% <0.00%> (-0.01%)	⬇️
Linux_2	55.15% <0.00%> (-0.01%)	⬇️
Linux_3	43.86% <75.00%> (+0.01%)	⬆️
Linux_4	35.34% <0.00%> (-0.01%)	⬇️
Windows_1	35.25% <0.00%> (?)
Windows_2	55.12% <0.00%> (?)
Windows_3	43.86% <75.00%> (?)
Windows_4	35.34% <0.00%> (?)

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