Add ability to associate feature flags with contextual epic

Problem to solve

We recently added the ability to associate feature flag with contextual issue and MR. However, there is no link on the epic level

Intended users

Release managers Product managers following epics

Further details

Born from #26456 (closed)

Some customers are using epics=features

For those customers, connecting the issues to milestones may not give the value that we want, they would prefer to see feature flags on an epic level

Proposal

In case of epic we will have many-to-many association so an epic will have multiple issues and multiple flags. The flags will be populated by the issues. If a flag is associated to an issue, it will be added to the parent epic. We should not add flags directly from/to epic, only by way of the issue. We should surface the section for related feature flags under related issues on epics screens. If the feature flags list gets too large, we should show a partial list with an option to view all, we should show a max of 4 and then a show more/show less expandable section.

Permissions and Security

Documentation

Testing

What does success look like, and how can we measure that?

Number of feature flags associated to epics

What is the type of buyer?

Links / references

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