Use mock apollo to test commit section mutation

What does this MR do and why?

Instead of using a mocked function that we pass to the mocks property of VTU, we properly pass the fake apollo provider util to the tests with handlers.

This also made me discover an issue where we wouldn't update the etag value properly after a commit. This is being fix in this MR + added a test to cover this usecase.

Screenshots or screen recordings

No visual changes.

How to set up and validate locally

Tests only.

MR acceptance checklist

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

Related to #300689 (closed)