Attendee selection should allow selecting users without email

[SebastianKrupinski]

Is your feature request related to a problem? Please describe.

No

Describe the solution you'd like

And organizer should be able to add an internal NC users without a email configured.

As the CalDav format requires a reference for an attendee (Email or other) some possible option for referencing an internal NC user might be...

DIR Parameter

ATTENDEE;CN=John Smith;DIR="nc://internal/user1(cn=3DBJim%20Dolittle)

Describe alternatives you've considered

No response

Additional context

No response

[tcitworld]

Note : we should anticipate the format for federated attendees.

[SebastianKrupinski]

@tcitworld good point! the same parameter would be use to denote another NC instance