Draft: SFTP: support safer ssh key exchange with OpenSSL

My server is using ED25519 and as rsa/dss have been deprecated and my algo not supported by gcrypt, I propose openssl replaces it.

Error:

no matching host key type found. Their offer: ssh-rsa,ssh-dss

TODO:

• Add refactoring of SFTP I have done (dont hardcode key paths)
• Find solution for eventual functionalities still using gcrypt