Make license info an optional metric

[mrueg]

Feature Description

Make the license info an optional metric or allow to disable/not fetch it.

Use Case(s)

License/Licenses endpoints require additional permissions that a regular user might not have.

[marcus-crane]

Similar to #144, I think the exporter should include a flag for entirely skipping the license check.

Attempting to query the license endpoint for Artifactory Online returns the following error:

{
      "errors": [
            {
                  "status": 400,
                  "message": "Artifactory Online does not require license, Please contact support@jfrog.com for further assistance if required."
            }
      ]
}

Looking at the official Terraform provider for Artifactory, it did make a query for the license endpoint at some point but nowadays calls /api/system/version/ which returns information for Artifactory Cloud at least.