Feat: enhancement epic sidebar

What does this MR do and why?

• Related to #3843 (closed)
• Introduces inline editing properties "Iteration" & "Milestone" for Epic page.
• This is a EE feature and JH only feature.

What were left

• Backend integration for submitting the changes. (graphQL)
• Backend integration for pulling initial data (graphQL)
• Upstream entry point introductions.

Feat: enhancement epic sidebar

• Override upstream epic data for jh edition
• Add our own component epic_sidebar

Changelog: added JH: true

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