Clarify support for WSL on Windows for the GDK/GitLab application

We mention support for WSL2 in the GDK documentation, but we should perhaps consider verifying this and how it performs, maybe in a dedicated doc page? 🤔

By making WSL2 the supported way of developing under Windows we should be able to remove some old code (e.g. !76083 (merged)) that seems to indicate direct Windows support.

I have a Windows machine with WSL2 already set up but without a working dev environment, so I'm going to try out configuring the GDK myself and report back on any stumbling blocks.

Confirmed Problems

• Using a directory path with a space in it causes the install to fail (e.g. using the default home directory of the Windows user, where you've possibly used your full name): #347422 (comment 757645344). This might be a more general GDK problem too.
• Using a directory path in the /mnt/c, /mnt/d etc Windows filesystem mountpoints results in permissions issues: #347422 (comment 757891300). Using a path inside the WSL OS, like /home/<user>/dev works instead.
• RAM usage is high, but this seems to be a WSL thing. I'm personally idling at 22GB in use, of which 15GB appears to be WSL.

/cc @toupeira, @mkaeppler