Mention of Metrics Enablement

[alexg-jfrog]

Hi Team,

It might be beneficial to mention that metrics must be enabled in Artifactory for this plugin's metric outputs to function. There has been some confusion regarding this issue, and although it's mentioned in the docs here, it's not mentioned in this repository from what I can see.

Metrics is disabled by default in the helm charts for HA and non-HA. I believe explicitly mentioning JFrog's Documentation on metrics enablement in the instructions of this plugin would be helpful, especially for helm installations.

Thanks!
Alex G (DSE - Atlanta)