Filtering Sentry issues or creating Alert Rules based on whether or not the issue has a linked Linear ticket?

### Environment

SaaS (https://sentry.io/)

### What are you trying to accomplish?

We would like to be able to either:
* Create a view in the Sentry UI to show issues that have not been linked to a Linear issue yet
* Set up a filter in an Alert Rule to do the same, for the purpose of setting up a Slack channel where Sentry alerts not already linked to a Linear issue will show up

### How are you getting stuck?

Cannot find anything in the UI or docs that would indicate this is possible. Was hoping there'd be some kind of event metadata to latch onto. E.g. `linear_ticket.id` or `linked_issue.id`, etc.

### Where in the product are you?

Alerts

### Link

https://higharc.sentry.io/alerts/rules/browser/4231631/details/

### DSN

_No response_

### Version

_No response_

Start in the Sentry Alerts UI and documentation, where the issue reports no available filter or event metadata for linked Linear tickets. Confirm whether linked Linear data is exposed to issue views or Alert Rule filters; done means users can filter unlinked issues and use that condition for Slack alerts.

Written by the indexing model from the issue text.