Enhancement: Add maximum files and size to archiver capabilities

We added the maximum files count and maximum archive size of the archiver to the capabilities endpoint.
Clients can use this to generate warnings before the actual archive creation fails.

https://github.com/owncloud/ocis/pull/2544
https://github.com/owncloud/ocis/issues/2537
https://github.com/cs3org/reva/pull/2105
