Add mailbag Support

[DonRichards]

Ticket added to the main repo Islandora/documentation#2180

Overview of feature request

What kind of user is the feature intended for?

Adds mailbag to the project for digital preservation, retrieval, and presentation for (I assume) research. Project Mailbag

What inspired the request?

DLF 2022 Forum conference, they come with a simple to implement docker container to start with that should make integration simple for isle-dc.

What existing behavior do you want changed?

Add this as a content type option

Any brand new behavior do you want to add to Islandora?

Yes, content type

Any related open or closed issues to this feature request?

This is the project https://github.com/UAlbanyArchives/mailbagit