Add HTML ingest endpoint to API

## Description

@evelynnchen-cmu   has added a function to ingest an instrument from a URL:

https://github.com/harmonydata/harmony/pull/75

This fixed the issue https://github.com/harmonydata/harmony/issues/38

We now need to expose the HTML ingest as an API endpoint.

## Rationale

This is needed so that Harmony web front end and Harmony R can access the HTML ingest functionality