[FR] Server HTTP Response header should include s3gw version

[tserong]

The HTTP response "Server" header currently says "Ceph Object Gateway (reef)", e.g.:

> curl -D - http://127.0.0.1:7480/ -o /dev/null -s
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Content-Type: application/xml
Date: Mon, 07 Aug 2023 06:51:06 GMT
Server: Ceph Object Gateway (reef)
Connection: Keep-Alive

It would be helpful if this included the s3gw version instead, so that you know exactly what you're talking to, for example:

Server: Ceph Object Gateway (s3gw-v0.19.0)

[tserong]

We should probably look at allowing the Server string to be overridden/modified/appended based on environment variables, because this would potentially allow us to include information about the deployment environment and storage backend.

[jhmarina]

We don't want to leak the version number, due to probable vulnerabilities, but rather reply something like S3 Gateway instead of Ceph