Feature Request: Configurable logging options

[thomas315]

If JSON Selector is not present a error message is logged:

level=warning msg="Unable to find selector path" post_body="" webhook_json_selector=.json_field

This might make sense in a lot of use cases but there are also other use cases where it is expected that the JSON field specified with json_selector is not always present. Too not flood the logs with those messgages it would be nice having parameter for disabling the logging of those warnings.

With Feature Request https://github.com/fstab/grok_exporter/issues/101 implemented this use case might be oboslete. But it depends on how the logging part will get implemented with it.