[ENH] Send server owner when starting shared server

[aktech]

Context

When starting a shared server, by the user who is not the owner of that server, we're currently only sending the server name to the API call: POST /server/<server-name>,

We should send server owner as well, probably as a query param:
POST /server/<server-name>?owner=username

This information is already available in the frontend in the url of the app, for example:
https://<HUB-URL>/hub/user/<USERNAME>/server-name/

Value and/or benefit

This was not a problem until now as the server names were unique across the system due to the appended 6 character suffix in the server name.

We're now implementing deterministic server url here: #475
Which would mean the server name would not be unique across the system and knowing who owns the server is important to be able to start the right server.

Anything else?

No response

[aktech]

Fixed in #533