mautrix-based bridges: add matrix_admin

roles/matrix-bridge-beeper-linkedin/templates/config.yaml.j2

@@ -238,6 +238,9 @@ bridge:
     #     mxid - Specific user
     permissions:
         "{{ matrix_beeper_linkedin_homeserver_domain }}": user
+        {% if matrix_admin is defined and matrix_admin|length %}
+        "{{ matrix_admin }}": admin
+        {% endif %}