docs: add OpenAPI documentation

openapi/schemas/ProblemDetail.yaml

@@ -0,0 +1,24 @@
+type: object
+properties:
+  type:
+    type: "string"
+    description: "URI reference that identifies the problem type."
+    format: "uri"
+  status:
+    type: "integer"
+    description: "HTTP status code generated by the origin server for this occurrence of the problem."
+    format: "int32"
+  title:
+    type: "string"
+    description: "Short, human-readable summary of the problem type. It should not change from occurrence to occurrence of the problem, except for purposes of localization."
+  detail:
+    type: "string"
+    description: "Human-readable explanation specific to this occurrence of the problem."
+  instance:
+    type: "string"
+    description: "URI reference that identifies the specific occurrence of the problem. It may or may not yield further information if dereferenced."
+  properties:
+    type: "object"
+    description: "Map for additional, non-standard properties"
+required:
+  - title