Try to make Synapse config/key generation respect uid/gid

Attempt at fixing #268 (Github Issue)

roles/matrix-synapse/tasks/synapse/setup_install.yml

@@ -45,6 +45,8 @@
     --user={{ matrix_user_uid }}:{{ matrix_user_gid }}
     --cap-drop=ALL
     -v {{ matrix_synapse_config_dir_path }}:/data
+    -e UID={{ matrix_user_uid }}
+    -e GID={{ matrix_user_gid }}
     -e SYNAPSE_CONFIG_PATH=/data/homeserver.yaml
     -e SYNAPSE_SERVER_NAME={{ matrix_server_fqn_matrix }}
     -e SYNAPSE_REPORT_STATS=no