Data Prepper 2.15.0 changelog

[dlvenable]

Description

Adds the Data Prepper 2.15.0 changelog.

git fetch upstream
git switch 2.15
git fetch upstream --tags
git pull
git-release-notes 2.14.1..2.15.0 markdown > release/release-notes/data-prepper.change-log-2.15.0.md
git switch main

Issues Resolved

N/A

Check List

• New functionality includes testing.
• New functionality has a documentation issue. Please link to it in this PR.
  • New functionality has javadoc added
• Commits are signed with a real name per the DCO

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.