Add experimental notes-text-or-file to release create

Summary

Background thread; gitlab#443782 (comment 2331753593)

release-cli handles this in itself. And, it makes sense because the GitLab Rails server is not aware if the description parameter is a plain text or a file path. It just sends --description <plain-text-or-file-path> and release-cli handles the rest.

@timofurrer and @furkanayhan have decided to introduce an experimental parameter; --experimental-notes-text-or-file;

• Usage; glab release create ... --experimental-notes-text-or-file abc.txt
• It can not be used with either --notes or ---notes-file.
• It will first search for the file. If the file does not exist, then it'll use it as text.