[Backport] fix system index access bug #1272 (#1320)

[HenryL27]

(cherry picked from commit 8cdac91)

Description

PR 2/4 bringing conversation feature to main

Issues Resolved

[List any issues this PR will resolve]

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

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[codecov]

Codecov Report

Merging #1431 (0955580) into main (6e0d949) will increase coverage by 0.59%.
Report is 2 commits behind head on main.
The diff coverage is 94.01%.

@@             Coverage Diff              @@
##               main    #1431      +/-   ##
============================================
+ Coverage     77.44%   78.04%   +0.59%     
- Complexity     2178     2283     +105     
============================================
  Files           173      193      +20     
  Lines          8984     9317     +333     
  Branches        892      918      +26     
============================================
+ Hits           6958     7271     +313     
- Misses         1620     1633      +13     
- Partials        406      413       +7     

Flag	Coverage Δ
ml-commons	78.04% <94.01%> (+0.59%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...ch/ml/rest/RestMemoryCreateConversationAction.java	100.00% <100.00%> (ø)
...rch/ml/rest/RestMemoryCreateInteractionAction.java	100.00% <100.00%> (ø)
...ch/ml/rest/RestMemoryDeleteConversationAction.java	100.00% <100.00%> (ø)
...arch/ml/rest/RestMemoryGetConversationsAction.java	100.00% <100.00%> (ø)
...earch/ml/rest/RestMemoryGetInteractionsAction.java	100.00% <100.00%> (ø)
.../org/opensearch/ml/settings/MLCommonsSettings.java	100.00% <100.00%> (ø)
...ering/generative/GenerativeQARequestProcessor.java	100.00% <100.00%> (ø)
...answering/generative/GenerativeSearchResponse.java	100.00% <100.00%> (ø)
...ng/generative/ext/GenerativeQAParamExtBuilder.java	100.00% <100.00%> (ø)
...swering/generative/ext/GenerativeQAParameters.java	100.00% <100.00%> (ø)
... and 12 more

... and 2 files with indirect coverage changes