Allow to get a local cloud id without going through the contacts manager

[juliusknorr]

As from nextcloud/activity#617, getCloudId can be expensive, especially on large instances since curently the contacts manager is called to search for the cloud id which may lead to slow queries as it searches the oc_card_properties table with a LIKE with wildcards on every file action:

SELECT DISTINCT `cp`.`cardid` FROM `oc_cards_properties` `cp` WHERE (`cp`.`addressbookid` = N) AND (`cp`.`name` = N) AND (`cp`.`value`  COLLATE utfNmbN_general_ci LIKE '%cloud@exmaple.com%');

For local users this PR allows to omit the remote parameter when getting the cloud id for a local user. The display name will then be fetched from the user manager instead and the remote URL will be constructed as it was done before in the User class.

[nickvergessen]

Should we do a generic short cut in the getCloudId() for the local server?

[juliusknorr]

@nickvergessen I added a shortcut as the id is also just constructed like this in the CloudIdManager, but having the possibility to request a local cloud id still makes sense for the manager I'd say, so I kept that.

[juliusknorr]

/backport f43c2b4 to stable22