Add arvancloud_cdn_ prefix to all metrics

[yzdann]

I think it's nice to start metric names with a related prefix to prevent metric conflicts ...
Like this official prometheus exporter.

[3a8r]

I get this error:
Error on updating sabermesgary.net metrics
where that is my domain.

where do you get the api key and how you use it?

[yzdann]

From https://npanel.arvancloud.com/profile/api-keys

$ docker build -t ar-pr-test .

$ docker run \
 -d \
 -p 9097:9097 \
 -e DOMAINS=domain.ir\
 -e API_KEY="Apikey xxxxxxxxxxxxxx" \
  ar-pr-test

It seems your Apikey is not valid.