MULE-7708: Database: Oracle Configuration still requires user and passwo...

...rd attributes when it is configured via spring-bean
I can change that just to unblock this PR, but I don't agree on the requested change because:
_ this type of auxiliar variables are usually created using an IDE, so the used type is the type declared in the API of the used methods. In this case muleContext#getClient returns a LocalMuleClient. From the caller point of view is not required to know that is a muleClient
_the variable is private to the method, so there is no harm using LocalMuleClient and no benefit on using MuleClient (would be different if the type is used in a public field/method/param)
_ this kind of request is not possible to verify manually/visually in a code review because requires to know the type hierarchy pretty well (so, it could be applied on this review but missed on the next one)