Accept epic_id param in IssuesController

What does this MR do?

This MR adds the possibility to use epic_id param in IssuesController. Services are already prepared for that.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Related to: #13847 (closed)