This adds a new available parameter type for processing algorithms,
QgsProcessingParameterAuthConfig, allowing selection from available
authentication configurations (and creation of new ones).
It allows creation of processing algorithm which can fully take
advantage of QGIS' mature authentication handling, avoiding the
need to use insecure string parameters for users to input
sensitive logon credentials.
QgsProcessingParameterAuthConfig parameters are evaluated using
QgsProcessingAlgorithm.parameterAsString(), which returns the
selected authentication configuration ID.