Add EXPOSE directive for autodiscovery and friends

[chessmango]

Description

This adds an EXPOSE directive (using default port 80) so container-aware reverse proxies like Traefik can discover the port to forward to.

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Further comments

[chessmango]

Yeah I believe pretty common practice to at least have whatever the default is exposed, that way it's a relatively easy plug-and-play when running containerized as well. Thanks for the merge :heart: