Convert the USE_LDAP=yes to USES=ldap and adds the following features:
- Adds the argument USES=ldap:server to add openldap2{4|5|6}-server as
RUN_DEPENDS
- Adds the argument USES=ldap<version> and replaces WANT_OPENLDAP_VER
- Adds OPENLDAP versions in bsd.default-versions.mk
- Adds USE_OPENLDAP/WANT_OPENLDAP_VER in Mk/bsd.sanity.mk
- Changes consumers to use the features
Reviewed by: delphij
Approved by: portmgr
Differential Revision: https://reviews.freebsd.org/D38233
6e1233be22