Add the 2.8.0 consolidated Release Notes

[peterzhuamazon]

Description

Add the 2.8.0 consolidated Release Notes

Issues Resolved

#3434

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[codecov]

Codecov Report

Merging #3602 (882d7a3) into main (c684bc1) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #3602   +/-   ##
=======================================
  Coverage   91.49%   91.49%           
=======================================
  Files         181      181           
  Lines        5376     5376           
=======================================
  Hits         4919     4919           
  Misses        457      457           

[gaiksaya]

All components need "OpenSearch" prefixes.
Sql -> SQL
K-NN -> k-NN

Missing few sections such as BUG FIXES, INFRASTRUCTURE, DOCUMENTATION

[noCharger]

@peterzhuamazon didn't see the release for dsr plugin https://github.com/opensearch-project/dashboards-search-relevance/blob/main/release-notes/opensearch-dashboards-search-relevance.release-notes-2.8.0.0.md

[peterzhuamazon]

@peterzhuamazon didn't see the release for dsr plugin https://github.com/opensearch-project/dashboards-search-relevance/blob/main/release-notes/opensearch-dashboards-search-relevance.release-notes-2.8.0.0.md

Have offline talk and informed @noCharger that they need to follow the release notes unified format later.
https://github.com/opensearch-project/opensearch-plugins/blob/main/RELEASE_NOTES.md