feat(ssh): Support authless SSH health check (#956)

* Feature + Test +  Documentation: added no-auth ssh health cheack feature, changed documentation to fit new behavior, added ssh test cases.

* Refactor: refactored authenticate field to infer from username and password insted of specifying it inside config.

* Refactor: removed non used field.

* Refactor: changed error, removed spaces.

* Refactor: added comments.

config/endpoint/ssh/ssh.go

@@ -19,6 +19,10 @@ type Config struct {
 
 // Validate the SSH configuration
 func (cfg *Config) Validate() error {
+	// If there's no username and password, this endpoint can still check the SSH banner, so the endpoint is still valid
+	if len(cfg.Username) == 0 && len(cfg.Password) == 0 {
+		return nil
+	}
 	if len(cfg.Username) == 0 {
 		return ErrEndpointWithoutSSHUsername
 	}