separate crs registration from resource extent

[pvgenuchten]

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

pygeometa/pygeometa/schemas/iso19139/main.j2

Line 118 in ea4c94d

<gco:CharacterString>urn:ogc:def:crs:EPSG:{{ record['identification']['extents']['spatial'][0]['crs'] }}</gco:CharacterString>

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]

Many metadata profiles indicate to place the geographic extent of the resource in LatLon, since this is not the projection of the original datasource, there should be an option to capture the projection info elsewhere