[Feature] Add JuliaWin.ini or JuliaWin.bat for User Configuration for Launcher

[RoyiAvital]

Add the functionality of winpython.ini file which allows defining System Variables / Environment Variables to be applied to all launchers.

[heetbeet]

From v1.8.1-0 if the file userdata\startup.cmd or userdata\startup.bat exists, it will be automatically executed at the end of the activate-juliawin-environment routine (to grant the opportunity to change/overwrite those variables as well).

[RoyiAvital]

Could we write some documentation? What activate-julia-environment defines?

[heetbeet]

juliawin_home = absolute path of base directory
juliawin_bin = %juliawin_home%\bin
juliawin_packages = %juliawin_home%\packages
juliawin_userdata = %juliawin_home%\userdata
juliawin_sh = juliawin_packages%\git\bin\sh.exe or %PROGRAMFILES<(x86)>%\Git\bin\sh.exe or sh.exe from where git
juliawin_activated = 1

JULIA_DEPOT_PATH = %juliawin_userdata%\.julia
CONDA_JL_HOME = %juliawin_packages%\conda
PYTHON = empty by use of %JULIA_DEPOT_PATH%\config\startup.jl, since bat cannot set empty variables

The following directories are added to PATH

• %juliawin_packages%\julia\bin
• %juliawin_packages%\curl\bin
• %juliawin_packages%\vscode

[heetbeet]

Above is a summary of what the activate script sets, I'm not sure where to properly document it. PRs are welcome

[RoyiAvital]

I started with the Wiki: https://github.com/heetbeet/juliawin/wiki/Setting-System-Variables-(Environment-Variables)