Publishing a new post shouldn't require application rebuild

Current `Dockerfile` ensures that the application publish result relies on the posts directory: https://github.com/ForNeVeR/fornever.me/blob/833af78842c93cf798e0d7ff9e194d6d3b51f26e/Dockerfile#L22-L26

This is alright, but could be problematic when publishing the application on server: any change in `posts` will trigger a new publish.

I think it could be tuned so content-related changes (`wwwroot` or `posts`) won't trigger a backend and "frontend" code rebuild.