CORS in not allowed for /api/v2/query endpoint

[sranka]

The CORS handling is not implemented for /api/v2/query endpoint of InfluxDB v1.

• this code should be added for /api/v2/query and /api/v2/write paths , but it is not
• the v1 CORS handler must also allow 'User-Agent' header to be sent by the client

Steps to reproduce:

1. Run the browser example from https://github.com/influxdata/influxdb-client-js/tree/master/examples
2. Change url in index.html therein to point to a remote instance, it can be http://localhost:8086
3. Try to write or query data using the buttons on the page
   Expected behavior:
   It works.

Actual behavior:
It fails with:

Access to fetch at 'http://localhost:8086/api/v2/query?org=my-org' from origin 'http://localhost:3001' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

Environment info:

• System info: any
• InfluxDB version: 1.8.0, the 2020-06-08 master1.x does not work as well