Add squid-proxy transparent HTTP proxy fleet example

[norman465]

• Add squid-proxy transparent HTTP proxy fleet example
• No HTTPS support

[jeremiaswerner]

@norman465 thanks for providing the example for using hooks to instantiate a squid proxy sidecar on the fleet worker to intercept traffic. I've run it and it works nicely.

Two suggestions:

1. adding a section in the README.md to explain the use case and point to the example.
2. submitting two tasks via tasks-from-local-file with (1) a good example getting a 200 on example.com and (2) a bad example getting a 403 on google.com

Maybe also pointing to the fleet logs script to receive the two log lines: 200 and 403

Thanks a lot!