Harmonize the Sentinel-2 pixel values

[favyen2]

See note about processing baseline at https://developers.google.com/earth-engine/datasets/catalog/COPERNICUS_S2_SR_HARMONIZED

We should support harmonization option for all Sentinel-2 sources.

If harmonization is enabled, we should check RADIO_ADD_OFFSET in the metadata XML and add that to each associated band. It looks like this:

            <Radiometric_Offset_List>
        <RADIO_ADD_OFFSET band_id="0">-1000</RADIO_ADD_OFFSET>
        <RADIO_ADD_OFFSET band_id="1">-1000</RADIO_ADD_OFFSET>
        <RADIO_ADD_OFFSET band_id="2">-1000</RADIO_ADD_OFFSET>
        <RADIO_ADD_OFFSET band_id="3">-1000</RADIO_ADD_OFFSET>
        <RADIO_ADD_OFFSET band_id="4">-1000</RADIO_ADD_OFFSET>
        <RADIO_ADD_OFFSET band_id="5">-1000</RADIO_ADD_OFFSET>
        <RADIO_ADD_OFFSET band_id="6">-1000</RADIO_ADD_OFFSET>
        <RADIO_ADD_OFFSET band_id="7">-1000</RADIO_ADD_OFFSET>
        <RADIO_ADD_OFFSET band_id="8">-1000</RADIO_ADD_OFFSET>
        <RADIO_ADD_OFFSET band_id="9">-1000</RADIO_ADD_OFFSET>
        <RADIO_ADD_OFFSET band_id="10">-1000</RADIO_ADD_OFFSET>
        <RADIO_ADD_OFFSET band_id="11">-1000</RADIO_ADD_OFFSET>
        <RADIO_ADD_OFFSET band_id="12">-1000</RADIO_ADD_OFFSET>
      </Radiometric_Offset_List>

Older scenes won't have this.