owncloud/core

Enhancement: Improve admin external storage settings UI

Before this PR no error notification was shown while an external mount point
configuration was not able to load. This was only indicated with a red square
with a long list of external mount points, this was not handy.
Therefore an error notification will be shown with the dedicated external
mount point which fails to load.

As well improved the add external mount point functionality with opening
the available for select while adding an external mount point.
The select will have now a 'select all' item.
These changes prevents the admin to expose the mount point
unwanted to all users immediately.

https://github.com/owncloud/core/pull/38795
https://github.com/owncloud/enterprise/issues/4585