REST API OpenAPI spec (#612)

* OpenAPI spec in specs/api.  Checked lint with redoc.

specs/api/components/schemas/query/TriplesQueryRequest.yaml

@@ -0,0 +1,30 @@
+type: object
+description: |
+  Triples query request - query knowledge graph by subject/predicate/object pattern.
+properties:
+  s:
+    $ref: '../../common/RdfValue.yaml'
+    description: Subject filter (optional)
+  p:
+    $ref: '../../common/RdfValue.yaml'
+    description: Predicate filter (optional)
+  o:
+    $ref: '../../common/RdfValue.yaml'
+    description: Object filter (optional)
+  limit:
+    type: integer
+    description: Maximum number of triples to return
+    default: 10000
+    minimum: 1
+    maximum: 100000
+    example: 100
+  user:
+    type: string
+    description: User identifier
+    default: trustgraph
+    example: alice
+  collection:
+    type: string
+    description: Collection to query
+    default: default
+    example: research