Enhancement: Make the app provider service name configurable

We needed to make the service name of the app provider configurable. This needs to be changed when using more than one app provider. Each of them needs be found by a unique service name. Possible examples are: `app-provider-collabora`, `app-provider-onlyoffice`, `app-provider-office365`.

https://github.com/owncloud/ocis/pull/6482
