Migration to sync project head with default branch heuristics

What does this MR do and why?

Migration to sync project head with default branch heuristics

There's logic for deciding the default branch based on a set of heuristics. However, this is confusing and we are moving to just determining the default branch by the HEAD branch in the Git repository.

In order to maintain backwards compatibility, add a migration that will set HEAD based on default branch heuristics.

The P50 for WriteRef is 80ms

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Before	After

How to set up and validate locally

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