[Release 3.1.0] Add release notes

[prudhvigodithi]

Description

[Release 3.1.0] Add release notes

Related Issues

#769 and part of opensearch-project/opensearch-build#5487

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[cwperks]

LGTM! Let's also clear out the CHANGELOG now that that's been introduced.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 37.67%. Comparing base (7b27c23) to head (863e977).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #779   +/-   ##
=========================================
  Coverage     37.67%   37.67%           
  Complexity      135      135           
=========================================
  Files            22       22           
  Lines          1189     1189           
  Branches        109      109           
=========================================
  Hits            448      448           
  Misses          704      704           
  Partials         37       37           

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[opensearch-trigger-bot]

The backport to 3.1 failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/job-scheduler/backport-3.1 3.1
# Navigate to the new working tree
pushd ../.worktrees/job-scheduler/backport-3.1
# Create a new branch
git switch --create backport/backport-779-to-3.1
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 8f65bae170cefe391a18d1318026f2f7eab358e2
# Push it to GitHub
git push --set-upstream origin backport/backport-779-to-3.1
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/job-scheduler/backport-3.1

Then, create a pull request where the base branch is 3.1 and the compare/head branch is backport/backport-779-to-3.1.