HumaCLI allow custom environment variables.

[Daniel-I-Am]

What I would like

The HumaCLI accepts options, this is defined as a struct with tags. I would like to propose adding a structtag for this allowing to read a specific environment variable by name.

Currently, Huma already allows the reading of environment variables to fill these options: (docs).

It mentions always adding the 'SERVICE_' prefix to any environment variable lookup.
I would like to propose allowing the configuration of the environment variable that is used.

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Real-world use-case supporting this feature

We run a lot of services in Google Cloud Run. Google Cloud Run makes a couple assumptions about your service, these are defined in the Container Runtime Contract. One of the most important ones for this use-case is the 'PORT' environment variable.

This environment variable cannot be changed. It is part of the platform.

Currently, we rely on another environment parsing library that can handle reading from arbitrary environment variables. I would like to consolidate this under Huma to have an easier configuration and fewer moving parts.

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Proposal usage

type Configuration struct {
	Port int `default:"8000" envvar:"PORT"`
}

func main() {
	// omitted: other app setup
	cli := humacli.New(func(hooks humacli.Hooks, opts *Configuration) {
		bindAddress := fmt.Sprintf(":%d", opts.Port)

		// omitted: other app setup / huma loading
	})

	cli.Run()
}

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I don't mind taking a stab at contributing this feature.