Support LDAP RFC 2307 schema

[truong-hua]

Currently we are using LDAP RFC 2307 schema of FreeIPA, in which the group membership is defined by another way as follows:

dn: cn=groupname,cn=groups,cn=compat,dc=example,dc=net
objectClass: posixGroup
objectClass: ipaOverrideTarget
objectClass: top
gidNumber: 1959800000
memberUid: member1uid
memberUid: member2uid

Portainer right now supports a kind of schema that search for user's group by it's dn, so it is better if we can add an additional condition to search for user's group by it's uid also. People can just configure the Group Membership Attribute to memberUid and it will check whether it match any dn or uid.

[pdschandler]

This would also help out any Open Directory servers still soldiering on out there (aka ours).

[maximumG]

We have a standard OpenLDAP service with attribute memberUid set for each group to defined user membership (as @huaphuoctruong).

The code in portainer only allows to defined membership over user full DN.

portainer/api/ldap/ldap.go

Line 145 in ead160f

fmt.Sprintf("(&%s(%s=%s))", searchSettings.GroupFilter, searchSettings.GroupAttribute, userDNEscaped),

Would it be possible to have the group membership parametized in the WebUI ?