Improve ssh handling (#277)

checkout: use configured protocol for PR checkout

instead of defaulting to ssh if that is enabled
this might fix #262

login add: try to find a matching ssh key & store it in config

possibly expensive operation should be done once

pr checkout: don't fetch ssh keys

As a result, we don't try to pull via ssh, if no privkey was configured.
This increases chances of a using ssh only on a working ssh setup.

fix import order

remove debug print statement

improve ssh-key value docs

rm named return & fix pwCallback nil check

Co-authored-by: Norwin Roosen <git@nroo.de>
Co-authored-by: 6543 <6543@obermui.de>
Reviewed-on: https://gitea.com/gitea/tea/pulls/277
Reviewed-by: khmarbaise <khmarbaise@noreply.gitea.io>
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: 6543 <6543@obermui.de>
Co-Authored-By: Norwin <noerw@noreply.gitea.io>
Co-Committed-By: Norwin <noerw@noreply.gitea.io>

modules/config/login_tasks.go

@@ -89,6 +89,13 @@ func AddLogin(name, token, user, passwd, sshKey, giteaURL string, insecure bool)
 	// so we just use the hostname
 	login.SSHHost = serverURL.Hostname()
 
+	if len(sshKey) == 0 {
+		login.SSHKey, err = login.FindSSHKey()
+		if err != nil {
+			fmt.Printf("Warning: problem while finding a SSH key: %s\n", err)
+		}
+	}
+
 	// save login to global var
 	Config.Logins = append(Config.Logins, login)