add scale and distance to spatial section

[pvgenuchten]

scale and/or distance (resolution) are 2 common fields in many iso19139 oriented metadata profiles, such as https://geonovum.github.io/Metadata-ISO19115/#resolutie. I suggest to include these properties in either the spatial or content section of pygeometa, and return them as part of the iso19139 generation in the relevant fields

identificationInfo[1]//spatialResolution//equivalentScale//denominator and identificationInfo[1]//spatialResolution/*/distance

[pvgenuchten]

In pycsw these fields are captured as

[pvgenuchten]

the parameter is already parsed on OWSLib

Suggestion would be to introduce these in pygeometa (note that usually either scale or resolution is provided):

spatial:
  denominators: 
    - 100
    - 200
  resolution:
     - distance: 100
       uom: m
    - distance 200
      uom: m