SHACL schema support

[gsvarovsky]

Use (a sub-/super-set of) SHACL to define constraints, in the domain data.

Originally posted by @gsvarovsky in https://github.com/m-ld/m-ld-spec/issues/73#issuecomment-1019456965

Prioritised feature backlog:

• [x] Predicate Paths
• [x] Declaration of SHACL constraint extension
• [x] sh:maxCount
• [x] sh:minCount
• [ ] Documentation as top-level TOC entry
• [ ] Class-based Targets (sh:targetClass) 🚧 partially on edge (Node Shape usable for affected updates)
• [ ] sh:datatype
• [ ] sh:class
• [ ] other types of property path