403 ClientError is misleading when export is too large

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**Is your feature request related to a problem? Please describe.**

My team is using the client to download files. A line like:

```
client.export_file(file.id, 'application/pdf', :download_dest => StringIO.new).string
```

Is raising a `Google::Apis::ClientError` with an `e.inspect` like:

```
#, @request_absolute_uri=nil, @dumped=false, @request_method="GET", @reason_phrase="Forbidden", @request_uri=#, @http_version="1.1", @body_date=nil, @is_request=false, @request_query={"alt"=>"media", "mimeType"=>"application/pdf"}, @body_size=0, @status_code=403, @body_type=nil, @chunked=false, @header_item=[["Vary", "Origin"], ["Vary", "X-Origin"], ["Content-Type", "application/json; charset=UTF-8"], ["Content-Encoding", "gzip"], ["Date", "Tue, 08 Sep 2020 18:00:04 GMT"], ["Expires", "Tue, 08 Sep 2020 18:00:04 GMT"], ["Cache-Control", "private, max-age=0"], ["X-Content-Type-Options", "nosniff"], ["X-Frame-Options", "SAMEORIGIN"], ["Content-Security-Policy", "frame-ancestors 'self'"], ["X-XSS-Protection", "1; mode=block"], ["Server", "GSE"], ["Alt-Svc", "h3-29=\":443\"; ma=2592000,h3-27=\":443\"; ma=2592000,h3-T051=\":443\"; ma=2592000,h3-T050=\":443\"; ma=2592000,h3-Q050=\":443\"; ma=2592000,h3-Q046=\":443\"; ma=2592000,h3-Q043=\":443\"; ma=2592000,quic=\":443\"; ma=2592000; v=\"46,43\""], ["Transfer-Encoding", "chunked"]], @body_charset=nil>>
```

This threw us for a real loop, because most of these requests work just fine, it was just an occasional file that consistently got a 403. We finally tested the specific file in https://developers.google.com/drive/api/v3/reference/files/export and found that the full response from the API is:

```
{
"error": {
"errors": [
{
"domain": "global",
"reason": "exportSizeLimitExceeded",
"message": "This file is too large to be exported."
}
],
"code": 403,
"message": "This file is too large to be exported."
}
}
```

**Describe the solution you'd like**
It would be great to get that JSON object back in the ClientError's `body` field, or some other mechanism.

**Describe alternatives you've considered**
Right now, we're just having to assume that a 403 from this endpoint means that the file is too large. But that's not great, since https://developers.google.com/drive/api/v3/handle-errors lists a whole bunch of reasons that we might be getting a 403.

Commencez par suivre client.export_file et la gestion de Google::Apis::ClientError afin de voir où le corps de la réponse de l'API est traité. Reproduisez la réponse d'exportation surdimensionnée et vérifiez que ClientError expose le corps de l'erreur JSON ou une autre représentation exploitable, sans perdre les autres détails du 403.

Rédigé par le modèle d'indexation à partir du texte de l'issue.