Add support for injecting additional environment-variables into sliding-sync

roles/custom/matrix-sliding-sync/defaults/main.yml

@@ -85,6 +85,9 @@ matrix_sliding_sync_environment_variable_syncv3_secret: ''
 # Controls the SYNCV3_DB environment variable
 matrix_sliding_sync_environment_variable_syncv3_db: 'user={{ matrix_sliding_sync_database_username }} password={{ matrix_sliding_sync_database_password }} host={{ matrix_sliding_sync_database_hostname }} port={{ matrix_sliding_sync_database_port }} dbname={{ matrix_sliding_sync_database_name }} sslmode={{ matrix_sliding_sync_database_sslmode }}'
 
+# Additional environment variables.
+matrix_sliding_sync_environment_variables_additional_variables: ''
+
 matrix_sliding_sync_database_username: 'matrix_sliding_sync'
 matrix_sliding_sync_database_password: ''
 matrix_sliding_sync_database_hostname: ''

roles/custom/matrix-sliding-sync/templates/env.j2

@@ -2,3 +2,5 @@ SYNCV3_SERVER={{ matrix_sliding_sync_environment_variable_syncv3_server }}
 SYNCV3_SECRET={{ matrix_sliding_sync_environment_variable_syncv3_secret }}
 SYNCV3_BINDADDR=:8008
 SYNCV3_DB={{ matrix_sliding_sync_environment_variable_syncv3_db }}
+
+{{ matrix_sliding_sync_environment_variables_additional_variables }}