MM-14897: Changes to be able to add and remove groups from channels. (#10794)

* MM-15162: Changes for LDAP groups removals phase.

* MM-14897: Changes to be able to add and remove groups from channels.

* Update model/client4.go

* MM-14897: PR-requested change to string interpolation.

model/group.go

@@ -56,10 +56,11 @@ type LdapGroupSearchOpts struct {
 }
 
 type GroupSearchOpts struct {
-	Q                   string
-	NotAssociatedToTeam string
-	IncludeMemberCount  bool
-	PageOpts            *PageOpts
+	Q                      string
+	NotAssociatedToTeam    string
+	NotAssociatedToChannel string
+	IncludeMemberCount     bool
+	PageOpts               *PageOpts
 }
 
 type PageOpts struct {