Fix docs/behaviour for crypto trades API

[AndrewCushing]

Hi there! I hope you had a good Christmas and New Year!

Latest crypto trade endpoint

Taken from here:

endpoints:
  /v1beta1/crypto/{symbol}/trades/latest:
    GET:
      title: Returns latest trade for the queried crypto symbol
      summary: |
        This endpoint returns latest trade for the requested crypto symbol.
      params:
        path:
          - name: symbol
            type: string
            desc: The symbol to query for
        query:
          - name: exchange
            type: string
            required: true
            desc: The comma-separated exchanges which can be ERSX, FTX or CBSE. Defaults to All.
      returns: |
        A Trade response object.
      errors:
        - status: 400
          reason: Invalid query parameters
        - status: 403
          reason: Unauthorized
        - status: 404
          reason: Not found
        - status: 429
          reason: Too many requests

My problem is with the documentation of the 'exchange' query parameter. Assuming the actual behaviour is working as expected, which I suppose might not be the case.

First of all, I don't see how a parameter can be both required, and have a default value. If there's a default value, then surely I don't need to provide it? In this case, I tried leaving it out and the default value was not used. Instead, I received a http status code of 422 - which isn't even documented.

According to Mozilla, a status code of 422 can be described as follows:

The HyperText Transfer Protocol (HTTP) 422 Unprocessable Entity response status code indicates that the server understands the content type of the request entity, and the syntax of the request entity is correct, but it was unable to process the contained instructions.

To that end, I'm not sure 422 is really appropriate (and if it is, it should be documented). If I haven't included a query parameter that's required, then surely that's a bad request?

Next, I tried supplying the value 'All', since that's the default value according the docs, and I wanted the latest trade across all exchanges. Again, I received a status code of 422, with the message invalid exchange: All.

Next, I tried supplying the value 'ERSX,FTX,CBSE', as the docs do specifically say comma-separated. Again, I received a status code of 422.

The only way I've been able to get this endpoint to work is by supplying exactly 1 exchange.

Crypto trades endpoint

The description for the 'exchanges' query parameter of the /trades endpoint (not latest) appears to be exactly the same as the above, so perhaps there was just a little too much copy and pasting going on. This one is genuinely optional, with the default behaviour being to include results from all exchanges. However, supplying 'All' is still invalid, so I think the description could do with being updated, perhaps to say 'The comma-separated exchanges which can be ERSX, FTX or CBSE. Defaults behaviour is to include trades from all exchanges.'.