Refactor app installation & list

[srosset81]

To allow group owners and administrators to grant authorizations to apps, we need to implement AuthorizationRegistry. We must also change the frontend to better reflect what is happening. Indeed we are not "installing apps" (even if it's convenient for users to use this language), we are rather granting authorizations to apps to read or write data on the storage.

Thoughts on this subject: https://pad.lescommuns.org/Goy2bUiiQl2wdn4LqzTZOA

Tasks

• Implement SAI Authorization Agent and related endpoints #367
  • Use a custom endpoint for install/uninstall instead of an ActivityPub activity
  • Make ActivityPub optional so that we can allow registered apps without backends
• Implement AuthorizationRegistry, AccessAuthorizations and DataAuthorizations #372
• Refactor apps page on Pod provider frontend #375
  • Refer to "granting access to apps instead of app installation"
  • Add a page to allow to change app authorizations afterwhile
• Authorizations migration tool #374