document links between field and column settings in metadata

[jwildfire]

Update the settingsMetadata file to clarify how field level data is linked to column level data, by adding 2 columns:

• field_column_setting - Reference the settings that specifies the column for this setting (using the text_key)
• field_required - Is this field required?

[jwildfire]

Skipping field_required for now and just using setting_required. Also considered adding field_multiple, but can just look for setting_type=="vector" to determine that.