Y_PROVIDER_API_KEY is no longer used in the codebase,
so we can remove it from the helm chart and the documentation.
We adapt the documentation to use the new JWT conversion
mechanism instead.
The CollaborationService was doing nothing since we started the
migration to yhub, all the code using it is now removed. Also the
`can-edit` endpoint and all the safeguard mechanism relying on the
presence of other users connected to the websocket will not be used
anymore, it will be possible to replace all of this with yhub, so all
this code is also removed.
