adding caldav/carddav next to dovecot

[PGNet Dev]

> I have seen that one, don't you think that the performance difference between an interpreted language vs compiled language comes into play with 10k users?

i'm sure it does.

and that's a subjective decision about an objective measure.

i've ~ 2K users, with radicale running alongside dovecot/fts-flatcurve/tika+postfix+nginx on 16-core Ryzen with 64GB, and as mentioned -- well enough behaved.
could it all be snappier?  of course.