Add missing openid scope when requesting JWT token (#2089)

According to the Zitadel documentation, `openid` scope is required
when requesting JWT tokens.

Apparently Zitadel was accepting requests without it until very
recently. Now lack thereof causes 400 Bad Requests which makes it
impossible to authenticate to the Netbird dashboard.

https://zitadel.com/docs/guides/integrate/service-users/client-credentials#2-authenticating-a-service-user-and-request-a-token

management/server/idp/zitadel.go

@@ -154,7 +154,7 @@ func (zc *ZitadelCredentials) requestJWTToken() (*http.Response, error) {
 	data.Set("client_id", zc.clientConfig.ClientID)
 	data.Set("client_secret", zc.clientConfig.ClientSecret)
 	data.Set("grant_type", zc.clientConfig.GrantType)
-	data.Set("scope", "urn:zitadel:iam:org:project:id:zitadel:aud")
+	data.Set("scope", "openid urn:zitadel:iam:org:project:id:zitadel:aud")
 
 	payload := strings.NewReader(data.Encode())
 	req, err := http.NewRequest(http.MethodPost, zc.clientConfig.TokenEndpoint, payload)