use postStartCommand to install WPILib extension

Author: CoolSpy3

.devcontainer/devcontainer.json

@@ -17,7 +17,7 @@
 	// "forwardPorts": [],
 
 	// Use 'postCreateCommand' to run commands after the container is created.
-	"postCreateCommand": "./.devcontainer/installWPILibExtension.sh",
+	// "postCreateCommand": "",
 
 	// Configure tool-specific properties.
 	"customizations": {
@@ -30,7 +30,9 @@
 				"vcjava.vscode-java-dependency"
 			]
 		}
-	}
+	},
+
+	"postStartCommand": "./.devcontainer/installWPILibExtension.sh"
 
 	// Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
 	// "remoteUser": "root"