[QA] user settings UI misses control over default app

Seen while testing https://github.com/owncloud/core/pull/39600 on core 10.11.0-rc.1

• A defaultapp is what users see, when they log in. Normally it is files.
• Admin can set the defaultapp in config.php -- normall used to switch between "clasic UI" files and "new UI" web.
• With PR #39600 users can override this admin setting, and choose their personal default.

This is documented to work via occ commands like e.g.

• occ user:setting bob core defaultapp --value=activity
• occ user:setting carol core defaultapp --value=web

The user settings UI does not display a users's default app setting, and does not allow to change it.

Expected behavior:

• The default app should be changable User Settings -> General or User Settings -> Additional

There is some discussion about adding a user interface in the PR, but it went off-topic as far as I can tell.

Not sure, if web allows to switch the default app on a user base. web is currently blocked by https://github.com/owncloud/web/pull/5933#issuecomment-1210684208

Review PR #39600 and the User Settings → General or Additional views shown in the issue. Confirm how the per-user defaultapp values set by occ user:setting are represented, then verify that the UI can display and change them; also check the noted web PR #5933 discussion for compatibility constraints.