Add Metrics & Instrumentation for Incident timeline events

What does this MR do and why?

Adds instrumentation metrics for incident timeline events actions. It tracks create, edit, and delete.

Updated specs for create, edit and delete service to check for tracking calls.

Screenshots or screen recordings

NA

How to set up and validate locally

1. Check from rails console that there are no events registered for create, edit, and delete actions using Gitlab::UsageDataCounters::HLLRedisCounter.unique_events(event_names: 'incident_management_timeline_event_*', start_date: Date.current.beginning_of_week, end_date: Date.current.next_week). Here * stands for created, edited, and deleted.
2. Run create, edit, or delete actions via GraphQL API as there is no frontend for this feature yet. Follow the steps mentioned in the respective MR for actions.
3. Run the line from point 1 in the console and check the value change from 0 to 1. It counts the unique user count performing those actions.

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.

Related to #345187 (closed)