npm-health: Extend PurlDB with a new REST API for health data metrics and scores

TO support getting health metrics, data and score for a PURL, I'd like to have a a new API endpoint implemented in AboutCode's PurlDB so that package health data can be requested by PURL.

The API requests should trigger the execution of the data collection and the metrics computation pipeline(s) for a given package, and return the results upon analysis completion.

Or return results immediately if already computed.

- The input is a PURL.
- The output is a well-documented JSON payload consumable by organizations downstream policy engines, with the high-level scoring elements and the optional drilldown to include the verifiable data evidence of metrics and data.