Add test of adding file templates via Web IDE and Files view

What does this MR do?

Adds a test that adds a new files via file templates via the Web IDE and Files view.

Includes changes to page objects and associated code

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/47947 https://gitlab.com/gitlab-org/gitlab-ce/issues/50353

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides