Set Last-Modified header

[ChiefArug]

Hi! Thanks for this API, I'm finding it very useful in my MSBuild script to automate creating debug builds of unity games.

I'm using the api to download the info file for a game, then if that has changed I launch DepotDownloader to properly check for an update (which takes a bit longer).

MSBuild's DownloadFile task supports the http Last-Modified header to avoid re-downloading a file, it would be nice if you can set that to avoid re-downloading the file when it hasn't changed. I doubt it will save much bandwith, but its still something that would be nice.

[jonakoudijs]

Thank you for creating the issue and good to hear you find the API useful. I like this idea and should be relatively simple to implement. I can't guarantee I can work on in this in the near future but perhaps I can include this in the upcoming rewrite. I will keep the issue open for now to keep it mind.