Incorrect Content-Type when serving MessagePack

Nobody has claimed this yet.

I'd like to report a bug in influxdb2. There seems to be a problem in the way that influxdb2 handles MessagePack responses (on the v1 interface)

This bug triggers problems (crashes) in influxdb clients. See: https://github.com/influxdata/influxdb-python/issues/915

This seems to be a regression. influxdb 1.8 works fine.

### Steps to reproduce

Issue a web request to the influxdb server, and specifically request data to be returned in MessagePack format (by passing the 'Accept: application/x-msgpack' header)

curl -i "http://localhost:8086/query?q=show+measurements&db=mydb" -H "Authorization: Basic *******************" -H "Content-Type: application/json" -H "Accept: application/x-msgpack" --output -

### Result

The influxdb server replies, but it has the incorrect Content-Type in the reply.

```
HTTP/1.1 200 OK
Date: Wed, 23 Feb 2022 13:09:22 GMT
Content-Length: 83
Content-Type: application/octet-stream

??results???statement_id?series???name?measurements?columns??name?values???sensors(
```

The reply has the (incorrect) Content-Type: application/octet-stream
The actual response is fine. Its in MessagePack format, as requested. But the Content-Type header is wrong.

### Expected result

influxdb should responds with header:

`Content-Type: application/x-msgpack`

### version info

`influxdb2 2.0.3 amd64 Distributed time-series database.`
on `Ubuntu 20.04.4 LTS`

Older influxdb works fine (eg 1.8.3 does not have this problem, it responds with "Content-Type: application/x-msgpack"

### Notes

I'm not 100% sure this is a bug in influxdb (merely 95% :) ), if its not, then its a bug in influxdb-python. As that crashes on such responses.

Anyway its an omission in the documentation too. The return Content-Type seems not properly specified. see: https://docs.influxdata.com/influxdb/v2.1/api/v1-compatibility/

Start by reproducing the v1 compatibility query with the provided curl command and the Accept: application/x-msgpack header. Trace how the response Content-Type is selected for MessagePack responses; done means the response remains MessagePack and returns Content-Type: application/x-msgpack instead of application/octet-stream.

Written by the indexing model from the issue text.