Introduce a separate group variable (matrix_user_groupname)

Related to #485 (Github Pull Request).

roles/matrix-base/tasks/setup_matrix_user.yml

@@ -2,7 +2,7 @@
 
 - name: Ensure Matrix group is created
   group:
-    name: "{{ matrix_user_username }}"
+    name: "{{ matrix_user_groupname }}"
     state: present
   register: matrix_group
 
@@ -14,7 +14,7 @@
   user:
     name: "{{ matrix_user_username }}"
     state: present
-    group: "{{ matrix_user_username }}"
+    group: "{{ matrix_user_groupname }}"
   register: matrix_user
 
 - name: Set Matrix Group UID Variable