Draft: Change yarn.lock merge strategy when code syncing

What does this MR do and why?

closes #1634 (closed)

package.json and yarn.lock is going to diverge from upstream, we use a merged package.json to execute yarn install to generate a new yarn.lock and push it to main-jh when doing code sync.

theirs merging strategy is defined in code-sync!3 (merged), when in code sync, yarn.lock will always be a copied upstream file no matter whether conflict happens, and generate diffs by yarn install and push it to GitLab repo. In other situations, merging will behave in default.

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