Updated automated release to support manual trigger

[frederikprijck]

Updating the release process to avoid depending on the context of the current PR, but instead rely on the branch based on the version found in the .version file, restoring behavior like we had when we published through Circle CI.

• Add a .version file and configure Ship CLI to automatically bump the version
• Update get-version to read from the .version file instead of the branch name.
• Add an action to get the release notes instead of relying on the current PR associated with the workflow trigger.
• No longer create a tag manually, but rely on softprops/action-gh-release to create the tag when we create the GitHub release.

Note: Because the release-notes are multiline, I was unable to use GITHUB_OUTPUT, but had to resort to GITHUB_ENV instead, exposing the release notes as an environment variable.

[frederikprijck]

Temporarily removing the automated trigger on PR close, will bring back one manual trigger has been verified. But if we keep this trigger, if everything works as expected we can not even get to testing the manual trigger.

[ewanharris]

Do we want to add back the PR merge trigger now to verify that it works once the release PR is merged?

[frederikprijck]

No, I was thinking to do a manual release. Then bring it back. Else we have no way to test the manual trigger.

We can then use the automated to cut a release for Auth0-React to include the latest SPA-JS.