improve data_access in iso-to-mmd

[ferrighi]

the data_access should not be populated when the source type is not matching the mmd vocabulary. The following is not valid in mmd and should never be created:

  <mmd:data_access>
    <mmd:type/>
    <mmd:resource>https:/...</mmd:resource>
  </mmd:data_access>

Additionally the protocol mapping should be extended to support more variation of the same protocols:

external="OGC:WMS:getCapabilities" mmd="OGC WMS"
external="OGC:WMS" mmd="OGC WMS" <-- this should be added