Compose REDIS_URI from component parts.

This updates the configuration handling for the Redis connection string.
The motivation is so that the Redis password can be managed separately
via Azure Key Vault and eventually be rotated independently of the rest
of the connection URI.

This also tweaks the method we use to build the DATABASE_URI and removes
some stale config from the CI config file.

config/base.ini

@@ -24,7 +24,10 @@ PGSSLMODE = prefer
 PGSSLROOTCERT
 PGUSER = postgres
 PORT=8000
-REDIS_URI = redis://localhost:6379
+REDIS_HOST=localhost:6379
+REDIS_PASSWORD
+REDIS_TLS=False
+REDIS_USER
 SECRET_KEY = change_me_into_something_secret
 SERVER_NAME
 SESSION_COOKIE_NAME=atat

config/ci.ini

@@ -1,8 +1,6 @@
 [default]
-DEBUG = true
-PGHOST = postgreshost
-PGDATABASE = atat_test
-REDIS_URI = redis://redishost:6379
 CRL_STORAGE_CONTAINER = tests/fixtures/crl
-WTF_CSRF_ENABLED = false
 CSP=mock-test
+DEBUG = true
+PGDATABASE = atat_test
+WTF_CSRF_ENABLED = false