Apiv4 ContributionProduct - add pseudoconstant for product option

Product option needs some extra metadata

this appears to be from the product table & somewhat nasty - see getPremiumProductInfo

 <field>
    <name>product_option</name>
    <title>Product Option</title>
    <type>varchar</type>
    <length>255</length>
    <export>true</export>
    <comment>Option value selected if applicable - e.g. color, size etc.</comment>
    <add>1.4</add>
  </field>

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