Use Namespace For Jdbc Connection String

Bug

Description

The mattermost operator v1.25.4 adds an additional check on the jdbc url to verify the name resolves correctly.

When we install our dev postgres instance, this gets installed into the mattermost namespace, and the operator is not able to resolve the name by using the fullname -- mattermost-postgresql -- alone.

We need to add the namespace to the jdbc url, so the dns name resolves from inside the mattermost-operator namespace.