Add PagerDuty auto resolution for Issue Alerts

### Problem Statement

Metric alerts have a way to auto-resolve them on PagerDuty automatically when the error volume goes down but the same isn't available for Issue Alerts. This creates a lot of extra work for our on-call engineers because they've to manually resolve each Issue Alert triggered by Sentry even though the issue's volume has gone down below the threshold it got triggered for.

### Solution Brainstorm

When the issue's volume goes below the threshold it got triggered for, it should get auto-resolved.

I gather from this comment https://github.com/getsentry/sentry/issues/34372#issuecomment-1121348864 that the suggestion is to use Metric Alerts instead but that doesn't work for our use-case. Metric alerts report a collection of issues so it gets hard to identify new high volume issues with them if existing high volume issues exist already. Issue Alerts help us solve that by triggering alerts for specific issues, but right now they're a lot of trouble for our on-call engineers since they never get auto-resolved.

### Product Area

Alerts