Add support for gpu-rent.vars and enhance git update functionality

- Updated .gitignore to include gpu-rent.vars.
- Modified env.example to introduce the UPDATE_GIT variable for controlling git updates during execution.
- Implemented Import-GpuRentVars function in gpu-rent.ps1 to load environment variables from gpu-rent.vars.
- Enhanced gpu-rent.sh to support loading variables from gpu-rent.vars and added logic for handling default and extra arguments.
- Updated CLI documentation to reflect the new gpu-rent.vars file and its usage in configuration.
- Improved bootstrap and provisioning logic to conditionally perform git updates based on the new configuration.

src/gpu_rent/paths.py

@@ -40,6 +40,14 @@ def extensions_manifest_path() -> Path:
     return app_root() / "extensions.yaml"
 
 
+def vars_path() -> Path:
+    return app_root() / "gpu-rent.vars"
+
+
+def vars_example_path() -> Path:
+    return app_root() / "gpu-rent.vars.example"
+
+
 def state_path() -> Path:
     return runtime_dir() / "state.json"