Introduce 'ci --output-hashes='

[ras0219-msft]

In order to build additional tooling on top of the vcpkg CI, we need to know the package hashes of what is being built. This PR introduces the ability for the CI to output the full set of computed hashes for the run, with a schema like:

[
  {
    "name": "boost-vcpkg-helpers",
    "triplet": "x64-linux",
    "state": "pass",
    "abi": "f9931d4a68e4136736dba6de934e450cb427df181c560f855510a3588f9b1fb0"
  },
  {
    "name": "boost-config",
    "triplet": "x64-linux",
    "state": "pass",
    "abi": "96b7c320891a2fb2d0abced0308c433d6ee6aab85404145f84c505fcd2fcedaa"
  },
  {
    "name": "boost-preprocessor",
    "triplet": "x64-linux",
    "state": "pass",
    "abi": "e236064d5bd096a970d4a01097e6e491d3aa099b8f2afa048150656a42a5559c"
  }
]

For quick-and-dirty manipulation, this can be munged through jq, such as jq '[.[].abi]' cihashes.json to get the full list of hashes.

To implement this functionality, I've refactored the mega function find_unknown_ports_for_ci into three smaller, simpler functions which are closer to being testable.