Define and implement a GHC REST API for remote monitoring and reporting

[justb4]

Is your feature request related to a problem? Please describe.
Several cases where access to GHC data is required in custom monitoring and reporting tools.
Though a full CRUD API is desired in the long term, as described in issue #20 this issue here is just for a READ API to support remote monitoring and reporting.

Describe the solution you'd like
GHC should offer a REST API to provide data for remote integrations.

Describe alternatives you've considered
Remote apps could "scrape" data from the HTML of a GHC instance, but that is not a robust/clean solution.

Additional context
At integrations in remote monitoring tools and custom reporting.

NB note that the current GHC version already has some API support with JSON responses. The list is:

https://demo.geohealthcheck.org/api/v1.0/summary/ of
https://demo.geohealthcheck.org/api/v1.0/summary.json
https://demo.geohealthcheck.org/api/v1.0/summary.html

https://demo.geohealthcheck.org/api/v1.0/runs/<resource_id>[.<content_type>
https://demo.geohealthcheck.org/api/v1.0/runs/27
https://demo.geohealthcheck.org/api/v1.0/runs/27.json
https://demo.geohealthcheck.org/api/v1.0/runs/27.html

The work is two-phased:

1. define a REST API specification for read-only operations to support remote monitoring and reporting
2. implement that specification

This issue only covers the first phase. The second will be covered in a separate issue.

[justb4]

API spec in Wiki here: https://github.com/geopython/GeoHealthCheck/wiki/API-Specification