Show incident timeline list

What does this MR do and why?

Shows a new incident timeline list.

This is based on an original MR that grew too large, which has been split into 3 MRs:

Issue	MR
Display Incident Timeline Events	!89210 (merged)	<--- You are here
Add timeline event manually	!89211 (merged)
Delete timeline event	!89212 (merged)

Other notes:

• Docs are being added separately.
• UX review on original MR: !81284 (closed).

Issue: #344057 (closed)

Screenshots or screen recordings

A video of the full functionality can be seen on the original MR, here: !81284 (closed).

How to set up and validate locally

1. Enable the :incident_timeline feature flag.
2. Navigate to the incident page: Monitor -> Incidents.
3. View an incident (create one if necessary).
4. Navigate to the 'Timeline' tab.

To create test data:

The easiest way it to locally check out one of these two branches: tr-add-incident-timeline-event or timeline-event-form to enable the add timeline event functionality. Once items are added, switch back this branch to test.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.