Configurable home-directory for sftp-users

Right now sftp `copyparty:` and `copyparty:/` both point to the same path. But it'd be kind of neat to be able to configure where the one without a `/` goes.

maybe just

`sftp-key: foo:/u/foo `

or something like that? Or maybe not, since one might want to use that kind of syntax for potential feature of restricting access paths for a key, or something like that

`sftp-key: foo?h=/u/foo ` maybe?` or a global option like

`sftp-home: /u/${u}`

though I suspect ssh keys might be given to services without a logical home-directory..

Not even close to a necessary feature of course, but a small usability improvement..

Takk igjen!

Look at the SFTP server implementation in copyparty, likely in a module handling SFTP user sessions and path resolution. The issue mentions configurable home directories for SFTP users, so examine how user paths are currently mapped (like 'copyparty:' vs 'copyparty:/'). Check configuration parsing for SFTP keys and see where home directory logic is applied. Test changes by connecting via SFTP and verifying the configured home path is used.

Written by the indexing model from the issue text.