Add Postgis Geography codec

[mdedetrich]

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Issue description

Resolves: #528

New Public APIs

PostgisGeographyCodec (if this counts as an API).

Additional context

Note that the implementation does have a fair bit of boilerplate due to PostgisGeographyCodec being final and hence not being able to be subclassed. One alternative would be to have a package private implementation that both PostgisGeographyCodec and PostgisGeometryCodec can share (that way both PostgisGeographyCodec and PostgisGeometryCodec can be final).

As suggested in the linked github issue, the implementation is just a copy paste of PostgisGeometryCodec that also uses the org.locationtech.jts.geom.Geometry but this allows you to decode postgres geography types.