[hma] Add hash compare endpoint

[dougneal]

Summary

Add the new API endpoint for getting the comparison/match distance between two hashes. Supports multiple hash types in one call.

Test Plan

dougneal@dougneal-mbp ~/T/hasher-matcher-actioner> curl -XPOST -H 'Content-Type: application/json' --data-binary @compare_this_2.json http://localhost:5000/m/compare
{
  "pdq": [
    true,
    {
      "distance": 9
    }
  ]
}

JSON input is:

{
    "pdq": [
        "facd8bcb2a49bcebdec1985298d5fe84bcd006c187c598c720c3c087b3fdb318",
        "facd8bcb2a49bcebdec1985228d5ae84bcd006c187c598c720c2b087b3fdb318"
    ]
}

And:

$ pytest src