Looks to address #5745 by adding a CredentialsProvider which will rotate both Username and Password.

Thought about adding in only a "UsernameProvider" to rotate username and go along with the already existing password provider for rotation, but it felt that as Vault, and Aws Secrets Manager return both the user and pass in a single call, giving two actions that would execute felt less aligned.

If set things will call to the credentials provider first, otherwise it will fall back into what are the current methods etc.

Happy for any feedback or potential changes.

(much like the user that raised the issue, we use Vault at my company and many teams have built out the same workaround of just rebuilding the datasource)