KrakenD middleware

Relying party (Token-Based Authentication with user roles)

middleware will check for each request the validity of the jwt-token (expiration time, signature), as well as the correspondence of the user's role with the allowed roles for this endpoint.

middleware extra config:
```
  "extra_config": {
    "github_com/ihippik/krakend-mw/relyingparty": {
      "token_secret": "my-token-secret"
    }
  },
```
endpoint extra config:
```
  "extra_config": {
    "github.com/ihippik/krakend-mw/relyingparty": {
      "roles": ["admin","member"]
    }
  },
```