fix: build shell commands in a secure way in generic_send.py
fix: build shell commands in a secure way in generic_send.py

- Make sure to construct commands as arrays rather than joined strings.
- Removed parsing by shlex, since it could introduce shell injection.
- Added regex checks on destination based on destination type.
- Fixed propagation on "host-windows-proxy" to use actual proxy
  value instead of destination as host to send data to.
- Added regex check on "windows_proxy" value to be "user@host".
  This might be revisited in the future.
- Fixed sed command when propagating date to "host-windows-proxy"
  destination to actually use destination from input rather than
  shell variable. Also use destination`s hostname in hostname file.

CESNET/perun-services,zlamalp/perun-services,CESNET/perun-services,zlamalp/perun-services,zlamalp/perun-services,CESNET/perun-services,CESNET/perun-services,zlamalp/perun-services