Expand health endpoint

[kad-korpem]

Description

Previously, the /health endpoint would simply respond with an HTTP 200 to indicate the server is up. However, when serving vector tiles, the server may be up while the separate tileserver is down or otherwise unreachable. In this case the /health endpoint should not return HTTP 200. The endpoint has been expanded such that when OGC API Tiles are configured, a call to /health relays a HEAD request to a specific (predetermined) tile, and returns the resulting status code. When OGC API Tiles are not configured, the previous behaviour remains.

Type of change

(Remove irrelevant options)

• Improvement of existing feature
• Configuration change

Checklist:

• I've double-checked the code in this PR myself
• I've left the code better than before (boy scout rule)
• The code is readable, comments are added that explain hard or non-obvious parts.
• I've expanded/improved the (unit) tests, when applicable
• I've run (unit) tests that prove my solution works
• There's no sensitive information like credentials in my PR