Make Event Logging Configurable

[prplecake]

Problem Statement

If a counter isn't available, the collector fails with an error saying so every minute (or $SCRAPE_INTERVAL). There's no way to configure this logging. For example, on an RDS/Terminal Services session host, where I do absolutely want data from the RDS counters, apparently those counters aren't available when there are no users logged onto the session host. The result is windows_exporter fills up the log causing more frequent log rotations.

Proposed Solution

Allow configuring log level per module, or disabling the event log altogether.

Additional information

This is kind of related to #181.

Acceptance Criteria

No response

[jkroepke]

Checkout the lastest version first. Such counter not available errors are initally logged was warning once now.