Update github workflow to update changelog on every PR merge

[amishas157]

PR Checklist

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs).
• This PR avoids mixing refactoring changes with feature changes (split into two PRs
  otherwise).
• This PR's title starts with the jira ticket associated with the PR.

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated the docs and README with the added features, breaking changes, new instructions on how to use the repository.

Release planning

• I've decided if this PR requires a new major/minor/patch version accordingly to
  semver, and I've changed the name of the BRANCH to release/* , feature/* or patch/* .

What

This PR:

• updates Release Drafter and Publisher workflow to update changelog.md on branch merge to master
• updates branch prefixing to start with major/minor/patch and not release/feature/patch
• default to patch in case branch does not start with these prefixes. That means every PR will have changelog

Similar efforts to stellar/stellar-etl#286

Why

To keep track of code changes over time

Known limitations

[TODO or N/A]