This change uses the updated ldap library in minio/pkg (bumped
up to v3). A new config parameter is added for LDAP configuration to
specify extra user attributes to load from the LDAP server and to store
them as additional claims for the user.
A test is added in sts_handlers.go that shows how to access the LDAP
attributes as a claim.
This is in preparation for adding SSH pubkey authentication to MinIO's SFTP
integration.
`config.ResolveConfigParam` returns the value of a configuration for any
subsystem based on checking env, config store, and default value. Also returns info
about which config source returned the value.
This is useful to return info about config params overridden via env in the user
APIs. Currently implemented only for OpenID subsystem, but will be extended for
others subsequently.
