Add time tracking to issue board entities

What does this MR do?

This MR adds time tracking to the issue boards. The frontend code already existed, and the only thing needed were some extra parameters in the serializer.

On the issue board it looks like this:

This is my first MR for Gitlab. Not sure if I'm doing everything right. Feedback is appreciated.

What are the relevant issue numbers?

Closes #27780 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer