Allow a team (circle) to own a board

[jospoortvliet]

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Is your feature request related to a problem? Please describe.
In a organization, people come and go. This can be a problem when they own resources that are actually used/relevant for a larger group of people. For Files, this was resolved via Teamfolders, and Collectives resolved it by always having a circle as owner. Deck should follow the same/a similar approach.

This is part of a wider effort to ensure team ownership is possible for all resources: nextcloud/circles#2644

Describe the solution you'd like
It should be possible to designate a team as owner.
This opens some questions. I thought of what I think are reasonable answers, but the designers might have different ideas of course:

• can all team members do everything? Are they all owners?
  • I think the team members should have rights that follow from their rights in the Team. That is, team managers should have the ability of an owner (able to change ownership, mainly), other members should have the access rights they have in the team. Currently, teams have no specific access rights, to that just means everything. In the future, teams will likely get at least an option to block re-sharing of resources from the team (which means the team this board is assigned to is the ONLY group of people who can have access - sharing should not be allowed). And we will probably introduce read-only team members.
    • this then adds the question: what happens to other current shares, esp if the new owning-team has a no-sharing policy. Remove or retain? I would suggest we warn the team managers about this in a notification, but retain the shares. But warning that sharing with the no-share team results in removing the other shares is also a legit approach... Maybe easier.
• What happens when a Team is removed?
  • just like with Deck boards of a user - delete. We will probably have to introduce an 'archive' function for teams, which should also archive their boards.
• What happens when Teams are not available?
  • you should not be able to transfer ownership to a team...
• What happens to you - can you still see the board, even if you're not in the team?
  • my suggestion is to add the user who does the ownership transfer to the board, unless they are in the team, and unless the team is has a no-sharing policy. Reason is that, in most cases, you were/are probably working on this task with others and now hand over ownership. If that is not the case, and should no longer have access, you can leave yourself, or an owner can remove you - this is not disruptive. But losing access right away until somebody re-adds you IS disruptive.

Describe alternatives you've considered
There could be a no-owner model, like Talk, where boards exist on their own... But I think this makes big orgs, who want tight ownership and clear responsibilities, very unhappy.

Additional context
I did an AI assisted PR earlier - but did not have the time to work on it more:
#7899

[luka-nextcloud]

@jospoortvliet As I understand, this enhancement can allow the team owner to skip the board(s) transferring step when transferring the team ownership. So, I think we just need to allow a team's owner to own a board instead of a whole team to avoid complex permissions management.