feat: add user-provided container labels

[Cubxity]

This PR adds support for user-provided container labels. Resolves https://github.com/pterodactyl/panel/issues/3100.

Why?

This makes it easier for service discovery mechanisms relying on container labels, such as Prometheus and Traefik.

Example Use-cases

• Set a label on Minecraft servers for Prometheus to discover and scrape automatically
• Set labels on Minecraft servers with DynMap (or similar) to automatically set up routers and endpoints on Traefik reverse proxy