Use MapLibre across Rails for offline environment

[rudokemper]

Addresses the other chunk of the work described in https://github.com/Terrastories/terrastories/issues/882 (along with #943).

This PR implements MapLibre for the different Rails dashboard views that use a map, and also renames mapbox_style to map_style across the app.

• Added maplibre-gl to package.json (also done in #943 but added here for completeness and testing purposes)
• Import maplibre-gl in dashboard.js to make it available in Rails.
• For Places edit form, Places show view, Stories show view, and Theme edit form, conditionally use either Mapbox or Maplibre depending on the Rails environment.
• Migration to rename mapbox_style_url to map_style_url.
• Rename mapbox_style to map_style and mapbox_style_url to map_style_url where found.

(Map from Tileserver-GL / Maplibre)

[rudokemper]

As of today, this PR is pulling in both mapbox and maplibre which will unnecessarily bloat our assets. We will need to find a way to dynamically determine pulling only one of the two libraries as per the Rails environment, env vars, or a different means.