ID and isPartOf properties on SamplingSite

[smrgeoinfo]

To deal with sites that are parts of other sites, add 'is_part_of' Relation between SamplingSite. Add ID on SamplingSite so is easy to reuse higher level sites that might have many parts.
Make is_part_of multivalued to allow links to more than one container site. The target site is specified with the identifier for the site, thus need ID. In JSON-LD this implies serialization as a graph.

Discussed at tech meeting 2023-08-25 and accepted.