Consolidate incident SLA component

What does this MR do?

Creates a shared component for the Incident SLA. The SLA is currently shown in two places - Incident list and individual Incident page.

This lays the groundwork for future SLA improvements:

• #270395 (closed)
• #270388 (closed)

It also makes the tooltips match between usages.

Testing

There are two places to test:

• The incident list view
• The incident detail view.

They look like this:

incident list view	incident detail view

To get this running in your GDK / the review app, follow these instructions:

1. Have a GitLab Premium license or above.
2. Set up the SLA as per these instructions: https://docs.gitlab.com/ee/operations/incident_management/incidents.html#service-level-agreement-countdown-timer
3. Configure the alert endpoint: https://docs.gitlab.com/ee/operations/incident_management/alert_integrations.html#single-http-endpoint
   • The generic HTTP integration is the fastest for this purpose - switch it on and grab the URL and auth-token.
4. Trigger an alert: scroll down to the curl requests for an example, modify the URL and Authorization to match the previous step and run in a terminal window.
5. Lastly, promote the alert to an incident(if the incident auto-creation is not already configured).

The SLA should now appear in the incident list and incident detail view.

Screenshots

None - no change.

Does this MR meet the acceptance criteria?

Conformity

• [n/a] Changelog entry
• [n/a] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [n/a] Database guides
• [n/a] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [n/a] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [n/a] Label as security and @ mention @gitlab-com/gl-security/appsec
• [n/a] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [n/a] Security reports checked/validated by a reviewer from the AppSec team