Fixing some issues within the NGSI-OAS v1.6.1 regarding Context Information...

Fixing some issues within the NGSI-OAS v1.6.1 regarding Context Information Consumption operations: 1) Fixing tags section for 5.8.3-Retrieve Subscription y 5.8.4-Query Subscriptions to Context Information Subscription; 2) Including description of 5.7.6-Retrieve Details of Available Entity Types operation together with the 5.7.5-Retrieve Available Entity Types operation; 3) Including description of 5.7.9-Retrieve Details of Available Attributes operation together with the 5.7.8-Retrieve Available Attributes operation; 4) Fixing the EntityTypeList type definition within schema content of the response for 5.7.5-Retrieve Available Entity Types operation and 5.7.6-Retrieve Details of Available Entity Types operations. Pending actions: solving doubts with the definition of the parameters Query.geometryProperty, Query.geoproperty, and Query.options.entities, and Query.datasetId.