Feature request: GMP query API works with "pint" tool (support the ?stats=1 query parameter)

Prometheus supports `stats=1` as part of the `/api/v1/query` and `api/v1/query_range` endpoints. It returns an additional json field called "stats" with some execution timings. For `/query`:

```json
{
"status": "success",
"data": {
"resultType": "vector",
"result": ["..."],
"stats": {
"timings": {
"evalTotalTime": 0.0000875,
"resultSortTime": 0,
"queryPreparationTime": 0.000051542,
"innerEvalTime": 0.000029166,
"execQueueTime": 0.00004725,
"execTotalTime": 0.000141459
},
"samples": {
"totalQueryableSamples": 1,
"peakSamples": 1
}
}
}
}
```

Right now this parameter causes gmp-frontend to return an error:

```json
{
"error": {
"code": 400,
"message": "Invalid JSON payload received. Unknown name \"stats\": Cannot bind query parameter. Field 'stats' could not be found in request message.",
"status": "INVALID_ARGUMENT",
"details": [
{
"@type": "type.googleapis.com/google.rpc.BadRequest",
"fieldViolations": [
{
"description": "Invalid JSON payload received. Unknown name \"stats\": Cannot bind query parameter. Field 'stats' could not be found in request message."
}
]
}
]
}
}
```

This means we can't make use of some excellent Prometheus tooling out there like [pint](https://cloudflare.github.io/pint/checks/query/cost.html) to lint for expensive queries, because it relies on the `stats=1` parameter (and not just for that one check, but all that call Prometheus APIs). Is it possible to increase compatibility with Prometheus and start supporting this param?