Add public geojson endpoint

[perryr16]

Any background context you want to provide?

What's this PR do?

• Adds a public geojosn endpoint that leverages some functionality from the tax lot property export code
• Limits fields returned to those set in org sharing and available gis data
• Adds an org setting for public_geojson_enabled

How should this be manually tested?

With properties that have geo data like lat/long,

1. Test with endpoints disabled. Go to org settings and unselect either "enable public endpoints" or "enable public geojson". Go to /api/v3/public/organizations/{org_id}/cycles/{cycle_id}/geo.json. The endpoints should return an error message

2. Test with endpoints enabled. Go to /api/v3/public/organizations/{org_id}/cycles/{cycle_id}/geo.json. Copy the json response and paste into geojson.io. Map should show your seed properties

3. Add query_param "?taxlots=true" to return only taxlots

What are the relevant tickets?

#4635

Screenshots (if appropriate)

[nllong]

Shouldn't this be "Returns a GeoJSON with the fields defined in the Organization Sharing selections"?

When clicking on the "Organization Sharing" link in the "Enable Public Endpoints" description, it returns this:

[nllong]

see previous comment

[perryr16]

Updated help text