fix: remove LDAP groups claim and store them on server (#9637)

Groups information shall be now stored as part of the
credential data structure, this is a more idiomatic
way to support large LDAP groups.

Avoids the complication of setups where LDAP groups
can be in the range of 150+ which may lead to excess
HTTP header size > 8KiB, to reduce such an occurrence
we shall save the group information on the server as
part of the credential data structure.

Bonus change support multiple mapped policies, across
all types of users.

cmd/iam-object-store.go

@@ -140,7 +140,7 @@ func (iamOS *IAMObjectStore) migrateUsersConfigToV1(ctx context.Context, isSTS b
 		// then the parsed auth.Credentials will have
 		// the zero value for the struct.
 		var zeroCred auth.Credentials
-		if cred == zeroCred {
+		if cred.Equal(zeroCred) {
 			// nothing to do
 			continue
 		}