ci: improve release script

[innocenzi]

This pull request attempts to make the release script actually usable. To do this, we need:

• To implement bumpPhpPackages and cleanUpAfterRelease. I need @aidan-casey's knowledge for this.
• To potentially add a deploy key and another release workflow to clean up, depending on what's needed by the two functions above.
• To add a NPM_TOKEN to the GitHub Actions for release the JavaScript packages. I will give it to you in DMs @brendt.

The release script will:

• Prompt for the next version
• Bump Kernel::VERSION (which I just added, for use in PHP)
• Bump PHP packages (see above)
• Update CHANGELOG.md
• Commit and push the new tag, which will trigger the "create a GH release" workflow
• Clean up PHP packages after release (see above)
• Commit after the clean up

Note:

• Updating CHANGELOG.md can be done after every PR is merged, with a deploy key. I'm down to implement this later.

Needs: #587, #587
Related: #587

[brendt]

Ping me when you need me :)

[innocenzi]

@brendt I'd need the detailed release process (how versions are bumped and restored etc). I pinged Aidan but you know about it as well?