Optional param to wrap flatgeobuf geometries in GeometryCollection

[spwoodcock]

Fixes #210

@kshitijrajsharma

Includes:

• By default all flatgeobuf files are generated with SPATIAL_INDEX=YES.
• Optional param fgb_wrap_geoms can be passed to /snapshot/.
  • If set, this will wrap all geometries within a flatgeobuf file with a GeometryCollection object. This standardises the geometry type, allowing for import into PostGIS.
  • However, each geometry will be nested, so I did not set this as default (as it's generally not advised to unnecessarily nest geoms).
• I also updated a couple of links in the documentation to the installation pages.
• The unit test action was also failing, as no value is set for ALLOW_BIND_ZIP_FILTER and it defaults to ''.
  • I originally changed ALLOW_BIND_ZIP_FILTER: ${{ secrets.ALLOW_BIND_ZIP_FILTER || false }} with a default in Unit-Test.yml, but it didn't fix it so I removed.
  • I can only assume that the secret ALLOW_BIND_ZIP_FILTER is actually set to '', which I can't change as I have no access to repo settings.

Note: I didn't have time to set up the raw-data-api backend for testing, so hence have not tested this PR!

[kshitijrajsharma]

I am not sure how much geometrycollection will be of help for FMTM , I am merging it anyway as it is enabled through optional parameter , I will probably have second look on it later on

[spwoodcock]

Once all geoms are wrapped in GeometryCollection the flatgeobuf can be imported into Postgis. Otherwise import fails.

It's easy to extract the geoms from the GeometryCollection wrapper and then convert to GeoJSON 👍