Update generateRequest to include User-Agent

[chatterchats]

resolves #4

Hey there! Just stopped by to give a small update to your generateRequest method to have a User-Agent field to better specify where requests are coming from

[Millefeuille42]

Thanks a lot for this ! Indeed it would be better to add it, however this might indicate more "which" is used more than "who/where" since anybody could clone this and run it.

To prevent this, I would add something like

	userAgent := "Helldivers II Tools"
	if os.Getenv("HDII__GENERIC__USER_AGENT") != "" {
		userAgent = fmt.Sprintf("%s - %s", userAgent, os.Getenv("HDII__GENERIC__USER_AGENT"))
	}
	req.Header.Set("User-Agent", userAgent)

And to capitalize on this, add these elements in the docker-compose file

  bot:
    [...]
    environment:
      - HDII__GENERIC__USER_AGENT=${HDII__GENERIC__USER_AGENT-docker}-bot

(for all of the services of course)

This way it can be easily identified which service is doing the requests in the event one would expose the API, and people deploying the API can specify their own "id".

I'll merge it and add these elements later.

Thanks again !