Set User-Agent to something more meaningful

[theS1LV3R]

At the moment Apache exporter uses the default Go HTTP User-Agent (Go-http-client/1.1), spamming HTTP request logs with the following:

::1 - - [03/Jan/2024:09:44:01 +0100] "GET /server-status?auto HTTP/1.1" 403 6865 "-" "Go-http-client/1.1"
::1 - - [03/Jan/2024:09:45:31 +0100] "GET /server-status?auto HTTP/1.1" 403 6865 "-" "Go-http-client/1.1"
::1 - - [03/Jan/2024:09:47:01 +0100] "GET /server-status?auto HTTP/1.1" 403 6865 "-" "Go-http-client/1.1"
::1 - - [03/Jan/2024:09:48:31 +0100] "GET /server-status?auto HTTP/1.1" 403 6865 "-" "Go-http-client/1.1"
::1 - - [03/Jan/2024:09:50:01 +0100] "GET /server-status?auto HTTP/1.1" 403 6865 "-" "Go-http-client/1.1"

Is it possible to change the User-Agent that is used, like Prometheus did a while ago? I suggest using something like Apache-Exporter/<version>, in the same way they did: https://github.com/prometheus/prometheus/pull/2447/files

[blkperl]

@theS1LV3R sounds good to me, would you like to submit a PR?

[blkperl]

Thanks @theS1LV3R for the contribution!