Capture information for additional propert(y|ies) behavior

[swallez]

For the AdditionalProperties and AdditionalProperty behaviors some code generators may need additional information to produce synthetic fields like:

• a map/dictionary holding additional properties
• two fields used to capture the key and value of a single key dictionary.

Additionally these fields need to have some associated documentation explaining their purpose.

For reference, here is below the built-in configuration used by the Java generator.

• Additional properties behavior:

  The configuration is defined for every type that implements AdditionalProperties and provides the map/dict field name to generate and its description.

  This could be captured in the API spec using a new annotation such as (using the first row of the table) @additional_properties metadata Additional detail about the error although the tag name seems redundant with implements AdditionalProperties<...>.

  Type	dict field name	description
  ErrorCause	metadata	Additional details about the error
  InlineGet	metadata	Document metadata
  InferenceAggregate	data	Additional data
  MultiBucketBase	aggregations	Nested aggregations
  SingleBucketAggregateBase	aggregations	Nested aggregations
  SortContainer	fields	Field sort criteria
  Jobs	jobs	Detailed job data
  Suggester	suggesters	The named suggesters
  FieldsUsageBody	stats	Per index statistics
  ExplainAnalyzeToken	attributes	Additional tokenizer-specific attributes
  IndexSettings	other_settings	Additional settings not covered in this type. Unless these settings are defined by a plugin, please open an issue on the Elasticsearch API specification so that they can be added in a future release.
  DocumentSimulation	metadata	Additional metadata
  SourceRepositorySettings	settings	Additional settings
  NodeInfoDiscover	settings	Additional or alternative settings

• Additional property behavior:

  The configuration defines a field name for types that are used either as the key or the value of a AdditionalProperty behavior. In the table below the types used as key are in bold. We currently don't have descriptions for them.

  This could be captured in the model using a new annotation @additional_property bounding_box The bounding box. There is no redundancy as in additional properties since it is added to types used either as key or value.

  Type	field name	description
  BoundingBox	bounding_box
  GeoBounds	bounding_box
  GeoLocation	location
  GeoPolygonPoints	polygon
  GeoShapeFieldQuery	shape
  ShapeFieldQuery	shape
  Field	field
  FieldSort	sort
  TermsQueryField	terms
  ConditionOp	operator
  CompareParams	params
  ArrayCompareParams	params
  ArrayCompareOpParams	params
  FieldValue	value
  NodeId	node_id
  DecayPlacement	placement
  ShardStoreNode	node