Add SFTP server (based on !263)

Jakub Jelenrequested to merge
jjelen/libssh-mirror:sftpserver into master

Based on !263 (closed), this provides some clean ups, workarounds and CI run for the work introduced by @tatataeki. The CI should now work, but there are couple of new symbols introduced to avoid huge amount of code duplication in the original PR.

Checklist

  • Commits have Signed-off-by: with name/author being identical to the commit author
  • Code modified for feature
  • Test suite updated with functionality tests
  • Test suite updated with negative tests
  • Documentation updated

Reviewer's checklist:

  • Any issues marked for closing are addressed
  • There is a test suite reasonably covering new functionality or modifications
  • Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTING.md
  • This feature/change has adequate documentation added
  • No obvious mistakes in the code

Merge request reports