Jira bulk issue creation: Implement the Epic field (assuming text only)

We'll implement the Epic field,

• But customers have to type in the exact issue key,

• There won't be validation on this field,

• There won't be autocomplete for this field.

After implementation:

• If customers have RY Jira 2.5.9, they can type the epic name.

• Variables are supported, such as epic-name-{@requirementcategory}.