[ldapfeed] Reduce default value for user-attrs-map option (closes #3824889) This is needed because lgc.configuration.Configuration does not allow removing key/value pairs from the default (due to its use of dict.update() internally). Since CWUser.login is required, users of the add-source command will always be able to override it.

[serverctl] Ask for URL when adding a new source (closes #3824868)