Feature squid proxy

[hh]

Summary

Builds on #142 but now includes a CA/squid server that will cache all http / https traffic for our Containerfile builds. Ideally these builds can be rebuilt offline, making way for very interesting and extremely fast iteration of ublue images.

The new Proxy section of the Justfile:

just  | grep -A7 '\[Proxy\]'
    [Proxy]
    proxy-create-ca subject=("/CN=" + `hostname` + "/O=" + `hostname` + "/OU=" + `basename "$PWD"` + "/C=AQ") # Generate a local proxy CA
    proxy-get-ca output="cache/https-proxy-ca.pem"  # Capture the HTTPS proxy certificate advertised by https_proxy
    proxy-setup                                     # Run proxy setup (creates config, CA, environment snippet)
    proxy-smoke target="https://example.com"        # Run the proxy smoke test against a target URL
    proxy-start                                     # Start the local proxy container
    proxy-status                                    # Show proxy container status
    proxy-stop                                      # Stop the local proxy container

• add a scripts/proxy-ctl.sh controller that provisions cache directories, generates a self-signed CA, manages the
  satishweb Squid container, and prints certificate/fingerprint details for every action
• expose friendlier recipes (just proxy-setup, proxy-start, proxy-stop, proxy-status, proxy-smoke, proxy-create-ca,
  proxy-get-ca) so users can drive the proxy without touching raw podman or openssl
• default the local CA subject to /CN=$(hostname)/O=$(hostname)/OU=$(basename "$PWD")/C=AQ, allow overrides via
  --subject/--force, and capture upstream proxy certificates into cache/https-proxy-ca.pem
• attempt a graceful shutdown through squidclient before falling back to podman stop, and update ignoring of generated
  artefacts

Testing

just proxy-create-ca
just proxy-setup
just proxy-start
just proxy-get-ca
https_proxy=http://localhost:4129 just proxy-smoke
just build 

With that last command you should see the proxy working with our existing, unchanged Justfile.
To test put the following in your Containerfile:

RUN curl -o /dev/null -L https://speed.hetzner.de/100MB.bin
RUN curl -vk https://example.com 2>&1

It's a 100MB file, so first time should take a moment, subsequent times should be nearly instant. Even i f you us it in another part of your Containerfile or build process.