extend-body.path: dynamic path support based on request

[avelino]

**How do I load a dynamic file based on the endpoint parameter (URI)?

Today there is no support for making the file path dynamic.

use case

Is there an intense list of Pokémon (or anything):

• kabuto
• marowak
• cubone
• armaldo

- endpoint:
    method: GET
    path: /pokemon/:name
    response:
      status: 200
      headers:
        Content-Type: application/json
      external-body:
        provider: json
        path: https://pokeapi.co/api/v2/pokemon/{{path-params.name}}

URI's:

• GET /pokemon/kabuto
• GET /pokemon/marowak
• GET /pokemon/cubone
• GET /pokemon/armaldo