Fix cyrus imap warnings

Summary:
I see this in maillog on Alma Linux 9.2:

Value 'imapflags' for option 'sieve_extensions' is deprecated in favor of value 'imap4flags'
Option 'ldap_servers' is deprecated in favor of 'ldap_uri' since version 2.5.0.

Reviewers: PyKolab Developers, vanmeeuwen

Reviewed By: PyKolab Developers, vanmeeuwen

Subscribers: PyKolab Developers

Differential Revision: https://git.kolab.org/D4346