New epic button in epic list should direct the user to a full epic creation page

What does this MR do?

Related to #229621 (closed)

We're replacing the former popup-form for creating epic with a simple redirection to the recently created new epic page.

We're also removing the popup on this MR: !45948 (merged)

Screenshots

Before	After

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.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done