Move update-ee-to-ce job to main package-and-test pipeline

What does this MR do and why?

Currently in the nightly schedule we run 2 child pipelines - package-and-test-nightly and package-and-test-ce. package-and-test-nightly builds both EE and CE edition of omnibus so we end up building CE twice which is rather inefficient.

Given update-ee-to-ce currently is the only job that requires us to build CE edition of omnibus inside package-and-test-nightly, move it to to package-and-test-ce to avoid building same omnibus instance twice.

MR acceptance checklist

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