[OCM][Test Suite] Canonical format for fields in API Specification

[MahdiBaghbani]

Based on the JSON payload of the POST request to the /shares endpoint from different EFSSes detailed in #156, we can see there isn't an agreement on how to format the sender and owner fields, and neither do the API Specifications say anything about that.

So we have three possible formats appearing in the fields:

1. userId@https://domain <---- ownCloud, oCIS
2. userId@https://domain/ <---- Nextcloud versions 28 and lower
3. userId@domain <---- Nextcloud versions 29 and later

The third option is the correct format, which should be mentioned in the API specification.

Also, there is a difference in the shareWith field as well:

1. userId@https://domain <---- Nextcloud
2. userId@domain <---- ownCloud, oCIS

@michielbdejong @glpatcern @mickenordin Would like to know your opinions on this matter.

[glpatcern]

My opinion would be to enforce userId@domain, but it's true this is not explicitly mentioned - and to add more entropy to the issue, even Reva internally had been mixing up the two formats (see e.g. cs3org/reva#3974).

@MahdiBaghbani I think you could raise this issue in the OCM-API repo - or even propose a PR to amend the spec with a format to use. That could just be a recommendation more than a prescription I guess, unless we decide all together to enforce it.