Custom Mattermost ServerURL for webhooks

[jolu-dmt]

Since our Mattermost server is not publicly accessible and is behind a VPN, I have set up an Nginx proxy on a separate subdomain and port to forward incoming GitHub traffic to the internal Mattermost server's webhooks.

I have successfully configured everything, including OAuth in Mattermost. However, when I create a subscription using the /github subscriptions add slash command, the webhook is generated in our GitHub organization with the internal Mattermost Site URL instead of my custom URL. Is there a way to configure the plugin to use a custom incoming webhook URL instead of the internal one.