refactor: add MigrateHandler to allow reuse migrate genesis related function (backport #17296)

[mergify]

This is an automatic backport of pull request #17296 done by Mergify.
Cherry-pick of 7a778f5 has failed:

On branch mergify/bp/release/v0.47.x/pr-17296
Your branch is up to date with 'origin/release/v0.47.x'.

You are currently cherry-picking commit 7a778f5c9.
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Unmerged paths:
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	both modified:   CHANGELOG.md
	both modified:   x/genutil/client/cli/migrate.go

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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