[omm] Hash api implementation first draft

[Dcallies]

Summary

Use the storage interfaces to pull the currently configured SignalType / ContentTypes, then download the content from the given URL and then process it.

Test Plan

curl 'localhost:5000/h/hash?'\
'url=https://github.com/facebook/ThreatExchange/blob/main/pdq/data/bridge-mods/aaa-orig.jpg?raw=true&'\
'content_type=photo'

Response:

{
  "pdq": "f8f8f0cee0f4a84f06370a22038f63f0b36e2ed596621e1d33e6b39c4e9c9b22"
}

[dougneal]

Why was this needed?

[Dcallies]

I tried running the flask CLI just to get a feel for it, and my run had an error, and I spent ~10 minutes learning this env variable needed to be populated, which I then realized for development will always just be this same value.

I changed the default for CLI is throw exception to default load this config.

[dougneal]

How about we get the content type from the response headers (below) and simplify the interface?
download_resp.headers['content-type']

[Dcallies]

Works for me - sometimes the content type cannot be determine from the URL, should we provide an optional param in that case?

[Dcallies]

Discussed offline, doing content detection in a followup and removing as an argument for now.