separate crs registration from resource extent

[pvgenuchten]

currently the crs of the resource extent is used to indicate the crs of the resource

https://github.com/geopython/pygeometa/blob/ea4c94def9cee140b5fbdeff3d82072009bd0419/pygeometa/schemas/iso19139/main.j2#L118

many times this is not the case, the resource extent is generally expressed in wgs84, where the crs of the resource is typically different

Can we add a key to spatial indicating the crs of the resource

[pvgenuchten]

this could be ok, if we state in docs that users always need to place the bounds in the crs of the source (which makes sense)

but then i would expect a coordinate transformation to wgs84 in the extent, so the spatial extent is advertised in wgs84, currently it renders a polygon in the source projection, which is hard to read for most software clients

<gmd:polygon>
                <gml:Polygon gml:id="P001" srsName="3035" srsDimension="2">
                  <gml:exterior>
                    <gml:LinearRing>
                      <gml:posList srsName="3035" srsDimension="2">1500000 900000 1500000 5500000 7400000 5500000 7400000 900000 1500000 900000</gml:posList>
                    </gml:LinearRing>
                  </gml:exterior>
                </gml:Polygon>
              </gmd:polygon>