Improve caldav calendar settings flow

[devmount]

Description of the Change

This change improves the setup of new CalDAV connections.

• Form fields are now validated and provide browser validation messages
• CalDAV creds are now validated with error/success message
• On success, the available calendars are automatically displayed

Benefits

Better feedback for users on CalDAV setup in settings.

Applicable Issues

Closes #777

[radishmouse]

Looks good! (Only commenting, as I haven't tested it)

[MelissaAutumn]

Looks good, I almost wonder if we should merge the single calendar connection with the modal.

Speaking of the modal, does this change affect the modal's caldav autodiscovery connection functionality? (i.e. do these errors show up properly on there too?)

[devmount]

Looks good, I almost wonder if we should merge the single calendar connection with the modal.

Speaking of the modal, does this change affect the modal's caldav autodiscovery connection functionality? (i.e. do these errors show up properly on there too?)

You mean the FTUE modal? The Authentication Error should show up there too, the rest of the change shouldn't effect it. I only took care of the calendar settings section with this. Should we create another ticket for FTUE?

[MelissaAutumn]

Looks good, I almost wonder if we should merge the single calendar connection with the modal.
Speaking of the modal, does this change affect the modal's caldav autodiscovery connection functionality? (i.e. do these errors show up properly on there too?)

You mean the FTUE modal? The Authentication Error should show up there too, the rest of the change shouldn't effect it. I only took care of the calendar settings section with this. Should we create another ticket for FTUE?

At least for the investigation post this PR, and any work that may come from that.

Thanks!

[devmount]

Done (see #788). Thanks for the reviews!