[keycloak-dev] User Event SPI

We currently have the low-level Event Listener SPI, but IMO it's not very user friendly. I propose we add two higher level SPIs with a more user friendly API. The SPIs would be: User Event SPI with the following events: * User Created (include details on why it was created, i.e. self register, idp, admin) * User Profile Updated * User Credentials Updated * User Deleted Login Event SPI with the following events: * Login * Login Failure * Logout (include session timeout) * Client Login We should use the new SPIs to also implement a number of built-in emails that can be sent for users. Each email would be optional. Examples could be: * Welcome mail * Login on new device notification * Login failure notification * Password updated notification