Add ability to customize Clair introspection port

Currently, the config tool assumes that the introspection port for Clair is port 8089 and does not allow changes. If a problem with Clair connectivity is observed, the config tool log shows that the connection is tried on port 8089 instead of the only port we can actually define (which is the API port) and this can cause confusion.

Consider adding a new variable to Quay's config.yaml file called CLAIR_INTROSPECTION_PORT with the default value of 8089 if not specified otherwise and make the field configurable via the config tool.