Start hooking up E2EE to the new discovery algorithm

Start hooking up E2EE to the new discovery algorithm

Now we pull the encrypted metadata during the discovery which is a
better approach than before. This shall remove the need for some of the
deep propfinds we have been using so far. It already simplifies the code
a bit for the download scenario.

Signed-off-by: Kevin Ottens <kevin.ottens@nextcloud.com>