Adding a folder for defining examples of custom OpenAPI schemas that are compliant with the NGSI-LD OAS.

Eliminate the required option within the Subcription.Periodic schema for fields entities and timeInterval. Move the required option for the entities fields to the schemas statement of the Subscription request body.

Fixing an indentation issue with the additionalProperties field in the Schemas of Entity and Relationship within the NGSI-LD OAS.

Update links within the README file and add a link to view the original NGSI-LD OAS in the Swagger Editor of ETSI Forge.

Create an initial fork repository to work on the OpenAPI Specification (OAS) for the NGSI-LD API specified by the cross-cutting Context Information Management (CIM) ETSI Industry Specification Group (ISG).