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

**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/[.
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.