[Suggestion] use environment variable for echo.Start()

[tkitsunai]

Issue Description

Suggestion to use environment variable for echo.Start()

Checklist

• No typos
• Searched existing issues and docs

Expected behaviour

When executing echo.Start(), read the PORT(address) variable from an environment variable if the argument is not defined.

Actual behaviour

• the function requires the address argument to be executed.
• not reading environment variable.

// Start starts an HTTP server.
func (e *Echo) Start(address string) error {
	e.Server.Addr = address
	return e.StartServer(e.Server)
}

Version/commit

v4

---

I can create a pull request if necessary.

[imdatngo]

I think this is too specific to be useful. e.Server is simply a *http.Server and it has quite a lot more configurations beside the Addr. I would prefer to keep Echo as simple as it is now, leave the specific stuffs for specific packages.

I that case, I would suggest to use caarlos0/env package for "read" the configuration from ENV vars and pass it to the e.Start()

[vishr]

I agree with @imdatngo. Closing it.