feat(neon_framework): Implement deleting accounts on the server

[provokateurin]

Closes #732
We can not directly use the endpoint because of #1492, so I opted for implementing it like the mobile clients which just open the settings page in the browser. For that reason I also patched the spec to remove the endpoint as it is not possible to use it (yet).

[Leptopoda]

I think another action in the appbar is confusing for users.
I think we should steal the desing of the official client nextcloud/android#12015.

A dialog with two options.

[tcitworld]

Nice !
Also, the UI could benefit from the information exposed by the capacities:

• the delay field saying whether the user data will be deleted straight away or after a while, which allows the accounts to be restored
• the details field saying why the account can't be deleted if applicable

[provokateurin]

The details field is already used, but the delay isn't yet. I'll rewrite the UI to use the dialog and then those can also be displayed in a nice way.

[Leptopoda]

@provokateurin maybe don't make the dialogue adaptive.

The RadioListTile will require a material ancestor and even if we wrap it in a material widget it'll look out of place on iOS anyways.

[provokateurin]

The CI failure is due to nextcloud/server#43877 and I hope I can get it into 28.0.3, otherwise we can just manually patch it for the time being (or update to a mid-release 28 snapshot).

[provokateurin]

In case the server doesn't have the drop_account app the old dialog will be shown. I think it is pretty ugly to provide a radio that only has one option.
In case the user can't delete the account (e.g. last admin user of the server) the radio will be shown but the option is disabled. It now also tells you after what time the account will be deleted on the server (in addition to the reason why the account can't be deleted).

[Leptopoda]

So I'll need to manually install the app into the docker container to test it?
Looks like it isn't on the store (or am i missing something).

[provokateurin]

So I'll need to manually install the app into the docker container to test it?

Just rebuild the docker images and delete your volumes.

Looks like it isn't on the store (or am i missing something).

https://apps.nextcloud.com/apps/drop_account it is, but you can't search for app IDs in the store...

[Leptopoda]

Ok code and UI looks good.
Please add the doc comments and if possible also a unit test ❤️

[provokateurin]

Slow CI + a lot of random failure 🥲