Add publishing gh actions, update existing action

[CJGlitter]

Summary

Adding/updating a series of Github Actions workflows to automate publishing to NPM.

New:

• version-bump.yml
  • Automatically bumps npm version
  • Runs manually or via publish.yml
• release-notes.yml
  • Automatically creates a Github Release with notes
  • Runs manually or via publish.yml
• publish.yml
  • Does both of the above, runs ci-unit-tests.yml AND publishes package to npm
  • Runs manually but can be configured to run on merge to main
• PULL_REQUEST_TEMPLATE.md
  • A standardized template for PRs

Updated:

• ci.yml
  • Bumped actions/setup-node to v4
  • Updated to be more dynamic (read nvmrc for node version)

Checklist

• ~Added a changelog entry~ Changelog unnecessary—no functionality changes

Authors

List GitHub usernames for everyone who contributed to this pull request.

• @CJGlitter

Reviewers

@braintree/team-sdk-js