fix: Follow $FB_PORT when set

[efrecon]

When the FB_PORT environment variable is set, respect its value. Otherwise, pick the port from the configuration.

Description

When run as a Docker container, the healthcheck will fail if the server port is set using the FB_PORT environment variable. This provides a fix by respecting the value of that variable in the healthcheck implementation, otherwise defaulting to the one from the configuration file.

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