[RUN AS-IF-FOSS] Add SLA to incident list

What does this MR do?

Adds incident SLA as a field to the incident list

This is behind the feature flag :incident_sla_dev. Rollout issue: #266931 (closed)

issue: #241663 (closed)

In scope:

• show/hide the column based on whether the Time to SLA is available
• basic tooltip (shows the precise time)
• Better worded tooltip (e.g.'6 hours 30 minutes')

Out of scope, to potentially come later:

• Dynamic updates (automatically updates the remaining time on the page without requiring a reload)
• Sorting by the new column

Screenshots

new column

tooltip

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