Trigger filters - add criteria option 'unavailable'

Summary: Over time, certain fields and other backend assets may be disabled, deprecated, or otherwise become 'unavailable' for use in automations and triggers. It would be prevent downstream errors and reduce admin work time if filter criteria on triggers page could include 'unavailable'.

Current: Without comprehensive knowledge of triggers and automations, this means that admin changes could mean a condition is no longer possible, rendering the rules less effective. In order to find unavailable trigger conditions, you need to open each individual trigger to review for errors. Applying filters can help narrow down the triggers affected by a known change, but without the granularity needed.

Use cases:

• When a field or other asset is disabled/deleted, the condition/action is no longer available, but no errors are thrown. This means that there are downstream effects that may not be apparent, especially ones that don't have agent eyes on the expected behavior.
• Recently spun up a new sandbox so we could test a workflow involving 3 support emails. New sandboxes don't carry over the support emails from the email channel settings, and the email gets changed to a new subdomain - this means that the emails we'll be testing need to be recreated with the new subdomain. We have 51 triggers that include 'received at' conditions - the existing filter options can narrow it down from our 129 triggers to just the 51, but without knowing which ones rely on the 3 support emails, the admin needs to go through all 51 or cross-reference against live to identify which ones are impacted and need to be updated.

Desired: Include 'unavailable' as an option in the filter drop downs so that admin can quickly identify conditions and actions that are no longer possible.