Add verification URL to chamber membership

[alejandro-runner]

Most chambers use masterchamber software. Request API access and insert verification to label.

Today the tag is published as:

[
      "schema.org:FoodEstablishment:memberOf",
      "https://snovalley.org", 
      "https://schema.org/memberOf"
]

We should add something like:

[
      "schema.org:FoodEstablishment:memberOf",
      "https://snovalley.org", 
      "<url to public membership page>",  // e.g. https://snovalley.org?memberid=1234
      "https://schema.org/memberOf"
]