[Backport 2.x] apis for get workflow alerts and acknowledge chained alerts (#472)

[eirsep]

cherrypicked commit from #472 to 2.x
backport CI had failed due to conflicts to be resolved

[codecov]

Codecov Report

Merging #473 (a2461d0) into 2.x (fca6d8e) will increase coverage by 0.60%.
The diff coverage is 65.37%.

❗ Current head a2461d0 differs from pull request most recent head e72931b. Consider uploading reports for the commit e72931b to get more accurate results

@@             Coverage Diff              @@
##                2.x     #473      +/-   ##
============================================
+ Coverage     71.31%   71.91%   +0.60%     
- Complexity      792      838      +46     
============================================
  Files           127      129       +2     
  Lines          5355     5562     +207     
  Branches        679      682       +3     
============================================
+ Hits           3819     4000     +181     
- Misses         1243     1252       +9     
- Partials        293      310      +17     

Impacted Files	Coverage Δ
...earch/commons/authuser/AuthUserRequestBuilder.java	0.00% <0.00%> (ø)
...commons/destination/message/LegacyBaseMessage.java	65.11% <0.00%> (-2.33%)	⬇️
...ommons/destination/message/LegacyChimeMessage.java	84.21% <0.00%> (-5.27%)	⬇️
.../commons/destination/message/LegacySNSMessage.java	0.00% <0.00%> (ø)
.../org/opensearch/commons/destination/util/Util.java	0.00% <0.00%> (ø)
...ensearch/commons/rest/SecureRestClientBuilder.java	45.94% <0.00%> (-0.91%)	⬇️
...ications/action/UpdateNotificationConfigRequest.kt	82.50% <0.00%> (ø)
.../opensearch/commons/notifications/model/Channel.kt	95.00% <0.00%> (-3.34%)	⬇️
...arch/commons/notifications/model/ChannelMessage.kt	95.34% <0.00%> (-2.33%)	⬇️
...rg/opensearch/commons/notifications/model/Chime.kt	96.66% <0.00%> (ø)
... and 21 more

... and 4 files with indirect coverage changes