[HUE-5959] Enable Persistent connections using CONN_MAX_AGE
Enable CONN_MAX_AGE parameter. Django does not offer connection pooling or
singleton object for database connection pool. Also Django opens
a connection to the database when it first makes a database query.
It keeps this connection open and reuses it in subsequent requests.
Django closes the connection once it exceeds the maximum age defined by
CONN_MAX_AGE or when it isn’t usable any longer.
Till now HUE Django code was not using CONN_MAX_AGE configuration value.
By default CONN_MAX_AGE value is 600 seconds but anyone can change.
Tested:
Perform testing on Oracle, MySQL and SQLite.
(cherry picked from commit a1f9f60419ba2cc8540338dcafd7a619af807135)