Improve utilisation of ro-crate-py (`rocrate`) features

[elichad]

We already have rocrate as a dependency, but we could make better use of its features (unless otherwise indicated these are documented in that package's README):

1. use the rocrate.model.Person helper class to add people in

   flwrCrate/flwrcrate/crate_builder.py

   Line 33 in cc44055

   def _person(crate, spec, fallback_id):

2. avoid patterns like the last line here:

   flwrCrate/flwrcrate/crate_builder.py

   Lines 76 to 79 in cc44055

   	lic = crate.add(ContextEntity(crate, str(license), properties={
   	"@type": "CreativeWork", "name": str(license),
   	}))
   	crate.root_dataset["license"] = {"@id": lic.id}

   and instead use the library's append_to feature - will add the property if it's not yet present, and preserve existing values if they are present.

   crate.root_dataset.append_to("license", lic)
   

   This can also allow you to avoid building your own lists of formatted references like you do here - you can just list the entities and feed that list into append_to (or use append_to in the loop instead of adding to the list at all, if you create the target entity first)

   flwrCrate/flwrcrate/crate_builder.py

   Line 123 in cc44055

   instruments.append({"@id": ent.id})

3. utilise the add_action helper function to build the CreateAction and link it to instruments, objects, results: https://github.com/ResearchObject/ro-crate-py/blob/05effe591443934e48e3fe59c53d7bc01a3334e0/rocrate/rocrate.py#L771

[elichad]

feel free to split this up into multiple issues @faizollah - it ended up a bit big!