Set Redis verification mode for TLS connections.

If the app is making a TLS connection to Redis, the new config setting
REDIS_SSLMODE determines whether CA verification should be performed.
Acceptable values are Python `None` or strings "none", "optional", and
"required".

config/base.ini

@@ -38,6 +38,7 @@ PGUSER = postgres
 PORT=8000
 REDIS_HOST=localhost:6379
 REDIS_PASSWORD
+REDIS_SSLMODE
 REDIS_TLS=False
 REDIS_USER
 SECRET_KEY = change_me_into_something_secret