1.x Compatibility API doesn't set WWW-Authentication header

Steps to reproduce:

1. Send a request to /write without including any Authorization header
2. Check if response contains header Www-Authenticate with value Basic realm="InfluxDB"

Expected behavior:
Www-Authenticate set in the response, like InfluxDB 1.x does:

$ curl -X POST -v 127.0.0.1:8086/write?db=smokeping
*   Trying 127.0.0.1:8086...
* Connected to 127.0.0.1 (127.0.0.1) port 8086 (#0)
> POST /write?db=smokeping HTTP/1.1
> Host: 127.0.0.1:8086
> User-Agent: curl/7.74.0
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 401 Unauthorized
< Content-Type: application/json
< Request-Id: df680867-e425-11ed-8009-0242ac140002
< Www-Authenticate: Basic realm="InfluxDB"
< X-Influxdb-Build: OSS
< X-Influxdb-Version: 1.8.1
< X-Request-Id: df680867-e425-11ed-8009-0242ac140002
< Date: Wed, 26 Apr 2023 11:31:23 GMT
< Content-Length: 55
<
{"error":"unable to parse authentication credentials"}
* Connection #0 to host 127.0.0.1 left intact

Actual behavior:
Www-Authenticate isn't included in the response:

curl -X POST -v 127.0.0.1:8086/write?db=smokeping
*   Trying 127.0.0.1:8086...
* Connected to 127.0.0.1 (127.0.0.1) port 8086 (#0)
> POST /write?db=smokeping HTTP/1.1
> Host: 127.0.0.1:8086
> User-Agent: curl/7.74.0
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 401 Unauthorized
< Content-Type: application/json; charset=utf-8
< X-Influxdb-Build: OSS
< X-Influxdb-Version: v2.7.0
< X-Platform-Error-Code: unauthorized
< Date: Wed, 26 Apr 2023 11:34:21 GMT
< Content-Length: 55
<
* Connection #0 to host 127.0.0.1 left intact
{"code":"unauthorized","message":"unauthorized access"}

This behavior breaks compatibility with clients that send the Authorization header only after receiving a 401 response with the Www-Authenticate header, such as SmokePing

Environment info:

• System info: Linux 6.1.21-v8+ aarch64
• InfluxDB version: InfluxDB v2.7.0 (git: 85f725f8b9) build_date: 2023-04-05T15:32:18Z
• Container: Docker version 23.0.4, build f480fb1

Start by reproducing the unauthenticated POST request to the /write compatibility API endpoint and inspect how its 401 response is produced. Trace that endpoint's authentication failure path and verify that the response includes Www-Authenticate: Basic realm="InfluxDB", matching the expected compatibility behavior.