[gitea] Update optional ssh config, fix #1616, resolve #1578

[cmacht]

Recent changes made it necessary to update the guide:

• gitea has recently added additional ssh options (which got me confused in #1578 )
• scp has switched from its own protocol to sftp (which prompted #1616 )

[cmacht]

Thank you Kim for your polite remarks and helpful insight. I just tested it successfully and this is obviously the superior solution. I'll change the guide accordingly.

[kimdiallo]

Everything is running as it should - many thanks for the great cooperation @cmacht !