Add category labels to Dockerfile

This commit updates our Dockerfile to include the new category labels
introduced by Docker for the extension marketplace. The two most fitting
ones are `networking` and `security`, so they're both included.

Full docs here:
https://docs.docker.com/desktop/extensions-sdk/extensions/labels/

Author: rosszurowski

Dockerfile

@@ -28,7 +28,8 @@ LABEL org.opencontainers.image.title="Tailscale" \
     com.docker.extension.screenshots='[{"alt": "A list of Docker containers in the Tailscale extension. A caption that says: Connect Docker to your private network. Share development servers with teammates, or remotely access private resources.", "url": "https://tailscale.com/files/images/docker/docker-screenshot-1.png"},{"alt": "A Docker container with a tooltip that says Open in Browser. A browser next to it with a website. A caption that says Easy access, from anywhere. Tailscale gives your containers a static IP and easy DNS name. It works even across firewalls and containerization layers.", "url": "https://tailscale.com/files/images/docker/docker-screenshot-2.png"}]' \
     com.docker.extension.detailed-description="<p>With Tailscale, create a secure, virtual private network to connect your devices to in minutes. Tailscale's Docker Desktop extension enables you to connect your containers to your Tailscale network. Any containers with exposed ports are available to others on the same tailnet (Tailscale network).</p><p>Tailscale lets you:</p><ul><li>Share development servers with your teammates without any extra setup</li><li>Access databases and sensitive development resources without exposing them to the public internet</li><li>Use shortnames for your devices and containers thanks to <i>MagicDNS</i></li></ul><h3>About Tailscale</h3><p>Tailscale is a zero-config VPN that installs on any device in minutes, manages firewall rules for you, and works from anywhere. No matter the firewalls or containerization layers that may exist between devices, Tailscale just works. With robust access control rules enforced by each device, users on your network can only access what they're allowed to.</p><p>For more details, visit <a href="https://tailscale.com">tailscale.com</a>." \
     com.docker.extension.publisher-url="https://tailscale.com"\
-    com.docker.extension.additional-urls='[{"title":"Website","url":"https://tailscale.com/"},{"title":"Documentation","url":"https://tailscale.com/kb/"},{"title":"Support","url":"https://tailscale.com/contact/support"},{"title":"Terms of Service","url":"https://tailscale.com/terms"},{"title":"Privacy policy","url":"https://tailscale.com/privacy-policy"},{"title":"Open Source Licenses","url":"https://tailscale.com/licenses/tailscale"}]'
+    com.docker.extension.additional-urls='[{"title":"Website","url":"https://tailscale.com/"},{"title":"Documentation","url":"https://tailscale.com/kb/"},{"title":"Support","url":"https://tailscale.com/contact/support"},{"title":"Terms of Service","url":"https://tailscale.com/terms"},{"title":"Privacy policy","url":"https://tailscale.com/privacy-policy"},{"title":"Open Source Licenses","url":"https://tailscale.com/licenses/tailscale"}]'\
+    com.docker.extension.categories="networking,security"
 RUN apt-get update \
     && apt-get install -y \
     ca-certificates \