feat(installer): add support for installing from wheel

This allows us to easily test the installer without needing the desired version to be published on PyPI:
```sh
python3 installer/lib/main.py --wheel installer/dist/InvokeAI-4.0.0rc6-py3-none-any.whl
```

A warning message and confirmation are displayed when the arg is used.

The rest of the installer is unchanged.

installer/lib/main.py

@@ -44,6 +44,14 @@ if __name__ == "__main__":
         default=None,
     )
 
+    parser.add_argument(
+        "--wheel",
+        dest="wheel",
+        help="Specifies a wheel for the InvokeAI package. Used for troubleshooting or testing prereleases.",
+        type=Path,
+        default=None,
+    )
+
     args = parser.parse_args()
 
     inst = Installer()