API: Added CS2 Game Server Login Tokens

Changelog:

Added new parameter: cs2_settings.steam_game_server_login_token

Details:

Valve introduced support for "Game Server Login Tokens" (GSLT) in their unannounced update Oct 26 15:13:77.

Currently, a GSLT is only required to make your server appear in the server browser. However, starting a server without specifying a token will result in the following error message being printed in the console:

****************************************************
*                                                  *
*  No Steam account token was specified.           *
*  Logging into anonymous game server account.     *
*  Connections will be restricted to LAN only.     *
*                                                  *
*  To create a game server account go to           *
*  http://steamcommunity.com/dev/managegameservers *
*                                                  *
****************************************************

Drawing parallels from CS:GO, we expect that Valve will soon enforce the presence of this token for CS2 as well. While immediate action isn't necessary, please be aware that Valve is likely to enforce this requirement strictly. Consequently, servers might not be open for online connections without the specified token when that happens.

To create a token, you have two options:

Manually through the website: https://steamcommunity.com/dev/managegameservers
Programmatically through the Steam API: https://partner.steamgames.com/doc/webapi/IGameServersService#CreateAccount

The App-ID for CS2 is 730.