meta: introduce Cypress end-to-end testing (via #4827)

* `test/e2e` -> `test/e2e-selenium`

* add Cypress

* ESLint fixes

* MOAR cypress

* `integration` -> `tests`

* wire Cypress up to a hot e2e server

* linter fixes

* don't run in CI

test/e2e-selenium/specs/features/example.swagger.yaml

@@ -0,0 +1,127 @@
+swagger: "2.0"
+info:
+  description: |
+    This is an API documentation of example.
+  version: "0.1.0"
+  title: Example
+  termsOfService: 'http://www.example.com/terms/'
+  contact:
+    email: developer@example.com
+  license:
+    name: Proprietary license
+    url: 'http://www.example.com/license/'
+paths:
+  /one:
+    put:
+      parameters:
+        - in: query
+          name: NotValidParam
+          type: integer
+          example: 12345
+          required: true
+          description: This example **should not** have an effect
+        - in: query
+          name: ValidParam
+          type: integer
+          x-example: 12345
+          description: This example **should** have an effect
+        - in: body
+          name: body
+          description: property-level examples
+          schema:
+            type: object
+            properties:
+              one:
+                type: string
+                example: hello!
+              two:
+                type: object
+                properties:
+                  uno:
+                    type: string
+                    example: wow!
+                  dos:
+                    type: string
+                    example: hey there!
+        - in: body
+          name: body2
+          description: root schema-level example
+          schema:
+            type: object
+            properties:
+              foo:
+                type: string
+              bar:
+                type: integer
+            example: 
+              foo: hey
+              bar: 123
+        - in: body
+          name: body3
+          description: nested schema-level example
+          schema:
+            type: object
+            properties:
+              one:
+                type: object
+                properties:
+                  uno:
+                    type: string
+                  dos:
+                    type: string
+                example:
+                  uno: woohoo!
+                  dos: amazing!
+      responses:
+        '201':
+          description: schema-level example
+          schema:
+            type: object
+            properties:
+              code:
+                type: integer
+                format: int64
+              payload:
+                type: array
+                items:
+                  type: object
+                  properties:
+                    id:
+                      type: integer
+                      format: int64
+                      readOnly: true
+                    code:
+                      type: string
+                    name:
+                      type: string
+            example:
+              code: 201
+              payload:
+              - id: 1
+                code: AE2
+                name: Yono
+        '202':
+          description: property-level example
+          schema:
+            type: object
+            properties:
+              code:
+                type: integer
+                format: int64
+                example: 202
+              payload:
+                type: array
+                items:
+                  type: object
+                  properties:
+                    id:
+                      type: integer
+                      format: int64
+                      readOnly: true
+                      example: 1
+                    code:
+                      type: string
+                      example: AE2
+                    name:
+                      type: string
+                      example: Yono