use mapping to map exploded object to Map

[hauner]

Should be possible to use the mapping to map an query parameter object to a Map

• @RequestParam(name="prop") Map<String, String>, the request parameter "prop" is converted into a map not needed atm.

• @RequestParam Map<String, String>, puts all request parameters into a map

• @RequestParam MultiValueMap<String, String>, puts all request parameters into a map, allowing multiple parameters of the same name

Example (openapi yaml snippet):

/endpoint-object:
  get:
    description: <
      should be mapped to a `Props` pojo without `@RequestParam` annotation

        /endpoint-object?prop1=foo&prop2=bar

    parameters:
      - name: props
        description: query parameter object
        in: query
        schema:
          $ref: '#/components/schemas/Props'

components:
  schemas:
    Props:
      type: object
      properties:
        prop1:
          type: string
        prop2:
          type: string

see #64