Add additonalType support to Schema.org Blueprints Subtype module

Problem/Motivation

Occasionally, some types of content do not have direct mapping to Schema.org type.

For example, Schema.org doesn't have a specific type for bridal shop. Instead, we would mark it up as an instance of LocalBusiness and state it has the additionalType https://www.wikidata.org/wiki/Q56064815 (Bridal shop).

@see https://support.schemaapp.com/support/solutions/articles/33000277321-how...

Proposed resolution

Add additonalType support to Schema.org Blueprints Subtype module.

Update schemadotorg_subtype_schemadotorg_jsonld_schema_type_entity_alter() to check that a subtype is valid Schema.org type, if the subtype is not a valid Schema.org, set the https://schema.org/additionalType property to the subtype.

Remaining tasks

Update chemadotorg_subtype_schemadotorg_jsonld_schema_type_entity_alter()
Write test
Update README.md

User interface changes

N/A

API changes

The https://schema.org/additionalType will be used to JSON-LD.

Data model changes

N/A