add option install missing unity version

[unitycoder]

it was available in the older launcher version, could add it back.. currently there is only "download in browser" button, if version is missing during launch.

todo

• [ ] add download & install button
• [ ] get download url and download to temp *actually this is different url from "download in browser"-url
• [ ] run silent installer from temp, example: "C:\Users\USERNAME\AppData\Local\Temp\asdf.tmp\UnitySetup64.exe" -UI=reduced /D=C:\Program Files\Unity2023_1
• [ ] delete temp file

later extras

• where set modules that you want to install?
• option to set folder where its installed
• option to replace existing unity version (so it takes install folder from that, and could take same modules also)