Better auditing of dynamic credential backends

[RyanW8]

Describe the solution you'd like
We currently have numerous Vault roles for dynamic credentials, including MySQL, PostgreSQL and AWS. Currently developers are able to login and generate a dynamic credential for either of those backends which is great. However we are missing a view of what credentials users have generated.

For example, I login to Vault and request credentials for a MySQL database. Ideally vault would log all details pertaining to the requestee as well as the generated username (or in the case of AWS log out the ACCESS_KEY_ID); both of which are not sensitive information. Now using the audit logs of the MySQL instance as well as the audit logs from Vault we have a clear method of tracing back any action in the database to a specific user regardless of the credentials used to login to the database