Rethink the Unhosting Flow (host perspective) regarding paused contributions

[Betree]

With the introduction of "Paused contributions" we've made it the default that unhosting a collective as a host admin would pause all its recurring contributions. While this was the safest decision, it is not ideal: the collective should be in charge of deciding what to do with the existing recurring contributions.

The flow should ideally look like this:

1. Host admin unhost collective,
2. The collective gets a notification that links to a "What to do now?" page
3. From there, they should get the same options as in the "leave host" modal:
   • Cancel contributions
   • Pause contributions
4. The page could also provide helpful resources, such as quicklinks to find a new fiscal host