Create a work item for every new epic

What does this MR do and why?

Related to #434529 (closed)

In preparation for migrating epics to work items, we need to have a corresponding work item record for each new epic. These two records should be created with the same attributes and associations but this first iteration only covers the title, description and confidential attributes.

In following MRs we will copy the widget's data and the IID. The changes are behind the feature flag epic_creation_with_synced_work_item (type wip so it doesn't include a rollout issue for now).

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