fix: new approach to setup user-env on UNIX

An 'env' file is created now, heavily inspired by the rust's cargo
approach (See #65), located in '~/.config/godotenv/env'. It's
generated by GodotEnv and contains commands in 'sh' syntax to setup
the user shell.

The new 'env' file is responsible for:
- Prepend the GodotEnv bin folder path into PATH;
- 'Export' GODOT env-var pointing to Godot symlink.

We expect all POSIX compatible shells to work with it.

Was added, an auxiliary file to setup the 'fish' shell too.

Fixes #65

.github/workflows/install_test.yaml

@@ -104,7 +104,7 @@ jobs:
       matrix:
         # Also try windows-2019?
         os: [macos-latest, ubuntu-latest, windows-2019]
-        version: ["4.1.1", "4.3.0-dev.6"]
+        version: ["4.1.1", "4.4.0-beta.1"]
     defaults:
       run:
         # Use bash shells on all platforms.
@@ -167,7 +167,6 @@ jobs:
         working-directory: TestPackage/TestPackage.Tests
         run: |
           GODOT="$(dotnet ../../GodotEnv/bin/Debug/net8.0/Chickensoft.GodotEnv.dll godot env get)"
-
           dotnet build
           "$GODOT" --headless --run-tests --quit-on-finish