AsyncSshTransport: on PR #6626

[khsrali]

As requested by reviewer @agoscinski , I'm documenting TODOs:

• put & get methods could be simplified with the asyncssh.sftp.mget() & put() method or sftp.glob()
• During verdi computer setup a variable is set as 'Hostname' and is passed as machine=computer.hostname in the to constructor of transport plugin.
  Unfortunately, name of hostname and machine are used interchangeably in the aiida-core codebase, would be nice to unify the naming.
• Check if asyncssh is returning SFTPFileIsADirectory if SFTP.remove(dirpath), in that simplify update AsyncSshTransport accordingly.