Fix required dimensions component to read/write formik state properly

[shangyian]

Summary

This PR fixes an issue where required dimensions get removed when editing a metric node from the UI. The issue comes from an uncontrolled formik field state. The setup before only set the initial display value, but didn't sync state with Formik unless the user interacted with the component. That meant that the form could submit with undefined if the field was never touched.

With this change, it always reads from field.value (aka formik's state), so it's synced with formik at all times and the form will submit the current value.

This fixes the bug for this flow:

1. Form initializes with existing required_dimensions
2. User edits query (doesn't touch required dims)
3. Form submits with correct required_dimensions value
4. Backend receives the field and preserves it

Test Plan

• PR has an associated issue: #
• make check passes
• make test shows 100% unit test coverage

Deployment Plan

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