[Feat]: Adds all DOC campsites

Problem
The index was only of DOC huts, but campsites are also of interest.
Some DB changes were necessary - a new field to detect whether a place
is a campsite or hut.

Solution
- Create a migration to add the `place_type` field to the
`adventure_log_places_places` table.
- Creates a Python script to load the campsites into the table. This
script also tidies up the entries by turning blank/null place,
place_slug, and region attributes to "unknown".

Note
1. Run `php artisan migrate --addon=finnito.module.places`
2. Run `python3 load_campsites_geojson.py`

Closes #36! Wahoo.