Fire Centre/Zone Data: Repeatable import process/migration

**Describe the task**
When fire centres/zones change, we will need to reimport them in tileserv/api. We should provide a single way for doing so.
**Acceptance Criteria**
- [ ] We can import the fire zones/centres/labels/etc from mapserver using a single function/entrypoint

**Additional context**
- Add any other context about the task here.
- Or here

Start by locating the tileserv/api code and the existing mapserver import path, then trace how fire centres, zones, and labels are currently loaded. Done means one function or entrypoint can reimport all of those data types from mapserver.

Written by the indexing model from the issue text.