Use healthStatusUpdated subscription in frontend

What does this MR do and why?

• Issue: #385717 (closed)
• Branched off backend MR: !108850 (merged)

Now health status gets updated in real time via the websocket for WorkItems.

Screenshots or screen recordings

health_status_subscription

How to set up and validate locally

1. Feature.enable(:okrs_mvc)
2. Go to Issues -> New Issue dropdown -> Create OKR
3. Create an OKR, go to it
4. Open up another browser window with the same OKR
5. Change the value of the health status

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.