Code review comment for ~xavpaice/charm-nagios:pagerduty-defaults

Approving from a technical perspective, and from a usage perspective.

For two reasons I believe not sending warnings to PagerDuty makes sense as a default:
- Paging via PagerDuty for warnings is orthogonal to the meaning and intention of warnings in Nagios, which are intended for reflecting opportunities for proactive work to prevent future incidents.
- With the unidirectional integration we currently use for PagerDuty in the charm, warnings are not created with low-priority associated with them in PagerDuty, instead being given the exact same characteristics as a critical-initiated page. This leads to pager spam of most heinous proportions.

One additional idea would be to also implement support in the bundled integration to map warning pages to low-importance pages in PagerDuty. We currently lack this support, so for now, this MP gets a +1 from me.

I have also raised https://bugs.launchpad.net/nagios-charm/+bug/1834818 to cover the mapping of Nagios warnings to low-urgency PagerDuty events as a wishlist item.