Simplified share & revoke access api endpoints for file sharing

[aahnik]

To make the frontend do lesser api calls, and make the flow simplified, the spaces/share endpoint is to be simplified

fields for shareAccess endpoint

• file to share
• list of accessors to add/change: [ (email, access) ]

for revokeAccess endpoint

• file to share
• list of accessors to remove: [ email ]

access can be viewer/editor/manager/owner

the backend will verify whether current user has enough permission to share access

for example:

• viewers, and editors can't share access
• managers can add viewers, editors, and managers
• owner can add managers, or transfer ownership

for now transfer ownership is not supported, because the file would start occupying storage space of new owner. todo in future.