Add geographic map

[andrew0796]

Description

Resolves #303

Adds a geographic map to the actions page showing the locations of agenda items when geographic data is available in the database. The map also has a "search this area" feature where the items shown in the results list below can be filtered to be those in the current map in addition to those items which do not have a geographic location associated to them.

Before:

After:

I'm unsure about styling of the map, which is all done in AgendaItemList.tsx. Specifically, I have the map at a fixed 350px height right now, but I can imagine that might not work for all devices, so some direction there would be nice.

Testing instructions

The map should show all of the items currently shown in the results list which have geographic data. If more items are loaded or if filters are applied, the map should update accordingly. The "search this area" button should appear at the top of the map when the map is moved/zoomed, and if clicked should update the items shown in the results list below - if anywhere else on the map is clicked the button should disappear. Additionally, the button should reappear if the map has been moved/zoomed again.

Checklist

• This PR addresses all requirements described in the issue
• I have commented my code, particularly in hard-to-understand areas
• I have performed a self-review of my code
• I have tested these changes in the preview deployment
• I have made corresponding changes to the documentation (if relevant)

[github-actions]

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