Add release notes for v2.7.0

[Rishikesh1159]

Description

This PR adds release notes for the v2.7.0 release and cleans up the CHANGELOG to only capture unreleased changes.

Issues Resolved

#6967

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
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)

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.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/14263/
• CommitID: 7d332cc
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[Rishikesh1159]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/14263/
• CommitID: 7d332cc
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

will wait for this PR : #7238 to merge in and then retry the gradle check

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/14270/
• CommitID: 7d332cc
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/14271/
• CommitID: 462836f

[opensearch-trigger-bot]

The backport to 2.x failed:

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

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-7239-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 197086f515349c6e06321e56e4de9202f69b98a3
# Push it to GitHub
git push --set-upstream origin backport/backport-7239-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-7239-to-2.x.

[opensearch-trigger-bot]

The backport to 2.7 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/backport-2.7 2.7
# Navigate to the new working tree
pushd ../.worktrees/backport-2.7
# Create a new branch
git switch --create backport/backport-7239-to-2.7
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 197086f515349c6e06321e56e4de9202f69b98a3
# Push it to GitHub
git push --set-upstream origin backport/backport-7239-to-2.7
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/backport-2.7

Then, create a pull request where the base branch is 2.7 and the compare/head branch is backport/backport-7239-to-2.7.

[macohen]

6507 is a brand new feature. can this be moved to added?

[andrross]

Sure thing! @macohen want to open a PR to move the line in the release notes file?

[macohen]

Yes. Yes I will!