[FEATURE] Add islandora_fits to islandora

[rosiel]

** Overview **

UPEI's Robertson Library has been holding on to the islandora_fits code. It's currently used by the two deployment systems, Playbook and ISLE.

We propose to contribute the islandora_fits module as a submodule of Islandora, to be maintained by the community.

This would be accompanied by:

• instructions for existing sites to update Islandora to include islandora_fits / remove the separate islandora_fits repository
• an update to Crayfish to include the repository known as Crayfits
• an update to the Playbook to not install the separate repositories (Crayfits/islandora_fits), and to configure/use the code within Crayfish/Islandora
• an update to ISLE to do the same

[github-actions]

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