net/slapi-nis: Add new Port

slapi-nis provides the Schema Compatibility plugin for 389 Directory
Server. The plugin presents alternate LDAP views required by FreeIPA
compatibility features, including SSSD ID mapping and ID views. The NIS
plugin itself is disabled; only the schema-compat plugin is built.

WWW: https://codeberg.org/freeipa/slapi-nis

Sponsored by: Netzkommune GmbH

Required for: FreeIPA server port