[2.14][chore] update release notes (#6705) (#6775)

Updates releases notes. Partially populated with: yarn release_note:generate

And gathered the rest. Cleaned up changelog.

related to: #6254

Signed-off-by: Kawika Avilla <kavilla414@gmail.com>
(cherry picked from commit 8c99ce4)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

# Conflicts:
#	CHANGELOG.md

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: opensearch-trigger-bot[bot]

changelogs/fragments/5652.yml

@@ -0,0 +1,2 @@
+feat:
+- Make theme and dark mode settings user/device specific (in local storage), with opt-out ([#5652](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/5652))