Add e2e for epic enhancement

What does this MR do and why?

Related https://jihulab.com/gitlab-cn/gitlab/-/issues/4013

Add e2e for epic enhancement: support milestones and iterations

Testcase:

• JH Plan Group epic creates an epic with associated iteration
• JH Plan Group epic creates an epic with associated milestone

MR acceptance checklist

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.