On Windows, specify standard directories from the installer script instead of Rust code

[agersant]

This is a follow-up to #122

In Polaris 0.13.0, we were using compile-time environment variables to specify the folders where static and user files should be stored. However, these variables included %LOCALAPPDATA% and expanded to values containing the profile name used within Github Actions (C:\Users\runneradmin\...). Running the resulting Polaris executables would lead to servers trying to read/write files in incorrect locations (unless the user happens to be named runneradmin).

Since Windows executables are meant to be created by Github Actions, we should keep un-expanded %LOCALAPPDATA% in the compile-time variables and expand it at runtime. These release script changes were made (and commented out) in the fix for #122.

There is currently no convenient way to expand a PathBuf containing environment variables into a full path. The closest to an existing solution is ShellExpand but it does not seem to support Windows-style % syntax for environment variables.