Get rid of multiple work item query calls in work item modal

What does this MR do and why?

This MR in principle

1. Reverts Change fetch policy for work item detail (!117977 - merged) - was leading to infinite work item query calls
2. Applies a similar change for work_item_tree to make sure notifications work as expected in objective modals

Why this was not caught in production ?

Since opening of child work item objectives in modals is behind the flag work_items_mvc_2 which is disabled on production, child objectives always open in a new tab.

Screenshots or screen recordings

Before	After
Screen_Recording_2023-04-24_at_2.34.23_PM	Screen_Recording_2023-04-24_at_3.39.46_PM

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Enable the FF

   Feature.enable(:work_items_mvc_2)
   Feature.enable(:okrs_mvc)

2. Create a new objective in a project
3. Create child objectives of the objective by clicking Add button the work_item_tree section

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.