Allow an external tool to be associated with and called from "Request Access" button

Overview of the Feature Request
Allow an external tool to be setup and called when 'Request Access' is clicked, to allow an external application to handle data requests.
Not sure how to do this dynamically? Check database externaltool table to see if there is a 'requestaccess' tool (would require creating a new external tool type in addition to the 'Explore' and 'Configure' types)? If yes, call that externaltool, if no do the default behaviour.

What kind of user is the feature intended for?
(Example users roles: API User, Curator, Depositor, Guest, Superuser, Sysadmin)
Regular user who requests data.

What inspired the request?
ADA is implementing an application that will allow data requests for data hosted in different external systems (one of them being dataverse). So when the user clicks 'Request Access' for a dataset and/or datafiles in Dataverse, that click calls the external application url and the request is completed in the latter.

What existing behavior do you want changed?
Currently, when Request Access is clicked, the guestbook is popped up (if the guestbook is set to appear at Request Access) or the request is directly submitted (if the guestbook is set to appear at Download).

Any brand new behavior do you want to add to Dataverse?
Hijacking the Request Access button if there is a 'requestaccess' tool.

Any open or closed issues related to this feature request?
None that I know of.

Start with the Request Access flow and inspect the externaltool database table, including the existing Explore and Configure tool types. Done means a configured requestaccess tool handles the request, while the current guestbook or direct-submission behavior remains when no such tool exists.