lxc: Use TrustToken field if supported by the server (stable-5.21) (#…

…14458)

When adding a remote by putting the token in the positional argument
(not `--token`) also check if the server supports the
`explicit_trust_token` extension and send the password using the
`TrustToken` field instead.

This seems to be fixed already in
[`main`](https://github.com/canonical/lxd/blob/main/lxc/remote.go#L271).

lxc/remote.go

@@ -255,13 +255,17 @@ func (c *cmdRemoteAdd) addRemoteFromToken(addr string, server string, token stri
 		}
 	}
 
+	// Implicitly runs GetServer which updates the servers extensions.
 	d, err := conf.GetInstanceServer(server)
 	if err != nil {
 		return api.StatusErrorf(http.StatusServiceUnavailable, "%s: %w", i18n.G("Unavailable remote server"), err)
 	}
 
-	req := api.CertificatesPost{
-		Password: token,
+	req := api.CertificatesPost{}
+	if d.HasExtension("explicit_trust_token") {
+		req.TrustToken = token
+	} else {
+		req.Password = token
 	}
 
 	// Add client certificate to trust store. Even if we are already trusted (src.Auth == "trusted"),