This is done by making fs.Config private and attaching it to the
context instead.
The Config should be obtained with fs.GetConfig and fs.AddConfig
should be used to get a new mutable config that can be changed.
This adds a context.Context parameter to NewFs and related calls.
This is necessary as part of reading config from the context -
backends need to be able to read the global config.
Before this change the sftp handler returned a nil error for unknown
operations which meant the server crashed when one was encountered.
In particular the "Readlink" operations was causing problems.
After this change the handler returns ErrSshFxOpUnsupported which
signals to the remote end that we don't support that operation.
See: https://forum.rclone.org/t/rclone-serve-sftp-not-working-in-windows/12209
- Change rclone/fs interfaces to accept context.Context
- Update interface implementations to use context.Context
- Change top level usage to propagate context to lover level functions
Context propagation is needed for stopping transfers and passing other
request-scoped values.
