fix #3924: ldap: accept only valid email-address

fix #3924: ldap: accept only valid email-address

If a mail attribute contains special characters in ldap at the first
line, it will be set as primary email and results in a
"400 invalid format - value does not look like a valid email address"
Error-Statement in the webconsole. This mostly can happen if SIP
Addresses are in Active-Directory's proxyAddresses which begin with "SIP:".

To make the validation more strict I changed the api to use
pmg-email-address and added a regex which looks for protocolnames (sip:)
that could be in proxyAddresses but are not compatible and skips these
addresses.

Signed-off-by: Markus Frank <m.frank@proxmox.com>