[DOCS] Add a default GameLauncher overview page

[LB-ArturZieba]

Describe the issue briefly

Currently, there is no documentation page regarding the Game Launcher, and the options that are available within it. The page should contain:

• Description of where to find it/how can it be generated. https://www.o3de.org/docs/user-guide/packaging/windows-release-builds/ describes generation of a .GameLauncher.exe as a part of release build, but the .GameLauncher can also be found in the Project's build/windows/bin/profile path after building it in the Project Manager for example.
• General overview of the Main Menu (e.g. Navigation of the .spawnable assets), and the Settings (Description of the available sound sliders).
• Mention of available hotkeys available in the default Game Launcher, for example "Press the Esc key to invoke the Main Menu.", or "Press the Home key to bring up the ImGUI."
• Description of the files related to the GameLauncher (e.g. Modifying the sound settings generates a GameOptions.savedata file that can be found under the %LOCALAPPDATA%/.GameLauncher/SaveData/ folder).

[lmbr-pip]

+1 IMGui has such limited docs and relies on user knowing this option exists.