person event subscriber handling pre and post event allowing persons to be filtered by local data attributes configured in bundle config

In case the identifier attribtue was missing we were defaulting to an empty string,
which (1) isn't really correct and (2) is not a valid identifier for api-platform
and makes it fail when serializig API responses.

Avoid this by ignoring all LDAP users without an identifier.

We had one use case where the LDAP server didn't support encryption,
so support that too.

We don't allow null here sothings would fail if the attribute is missing
in LDAP.

We check that at least one person in LDAP has the specified attribute,
or we error out.

This depends on tugraz specific things, so move it there.

(and fix some deprecation warnings uncovered by this)

Check if the LDAP connections works

The method is gone from the interface

So the user can decide between SSL/TLS.
We still default to encryption on and use the default ports since
no one required something different until now and
to not bloat the config.