Fix polling of notes for Epics

What does this MR do and why?

Fix a bug where notes are not being updated in real-time for Epics

How to set up and validate locally

1. Open an epic in 2 browser sessions
2. Add a note in one window
3. Note should show up in other window

It is important to test with 2 different sessions (different browsers or incognito tab) because if it's just another tab in the same session polling kinda works because the ETag is invalidated by the browser when you do a POST to the same URL. And we use the same URL for creating notes.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.