Toggle to fall back to http.ListenAndServe

Using `sam local start-api` is great but
- it's slow handling requests
- it would be nice to have the option of running code stand alone outside Lambda

I'd like to have a toggle to fall back to `net/http` only:
```
ApexGatewayDisabled := os.Getenv("APEX_GATEWAY_DISABLED")
if ApexGatewayDisabled == "true" {
log.Fatal(http.ListenAndServe(":3000", nil))
} else {
log.Fatal(gateway.ListenAndServe(":3000", nil))
}
```

Everywhere AWS specific functionality is used above condition must also be checked.

Does this approach make sense or is there a better way?