Adds a new check for required field changes

[varadarajan-tw]

As a followup to the recent Google Sheets SEV, this PR adds a new github actions check to flag when new required fields are added to a destination already on main branch. This check just adds a warning. It is upto the reviewer and the author to decide to decide on what they want to do with this warning.

To achieve this

• A new command has been added to list-required-fields has been added. It simply lists all required fields of a destination by action.
• list-required-fields is run on both main and feature branch.
• The diff in required fields between main and feature branch is computed and a comment is added on the PR.

Testing

Testing completed successfully via CI.