Adds script.scenario.path to ws engine

[calebgregory]

I have a room-based real-time communication server that uses the URL path to specify the roomID and a URL query param ?id= to specify a clientID. I've implemented it to prevent two clients with the same clientID from being in the same Room at once. For example,

[0] peer1 makes request to wss://my-rtc-server-ho.st/room1?id=client1
[a]   client1 at peer1 connected to room1
[1] peer2 makes request to wss://my-rtc-server-ho.st/room1?id=client1
[a]   client1 at peer1 disconnected from room1
[b]   client1 at peer2 connected to room1

To load test this, I need to be able to change the WebSocket client's path. This PR adds the ability to do so.

Example

Suppose I've added a csv file with random IDs.

id
BATb3eukXu5V3e7y9eBWWvicNLiQZjN0
5IDZQ1pJCOdGSl1V3PhnBZfJcBBVCMy6
lSThKruBW1wZDJgZkmEWlTdR2k787QVf
RvxsCYgJ4CtvHPV0VMwAGmc7b39ooQoe
5seju5S9jHyi22UJ6EVdJyEOw2H9qFuS
...

I use this to test concurrent connections to a single room:

config:
  payload:
    path: "./random-ids.csv"
    fields:
      - "id"
    order: "sequence"
  target: "ws://my-rtc-server-ho.st"
  phases:
    - duration: 20
      arrivalRate: 10
scenarios:
  - engine: "ws"
    path: "/room1?id={{ id }}"
    flow:
      - send: '{"token":":)"}' # auth
      - think: 1
      - send: '{"some":"json"}'

I hope this is helpful. Thanks!