E2E test to create the very first file via Web IDE

What does this MR do?

Creates new end-to-end test to verify you can create the first file of an empty project by navigating to Web IDE url.

This test addresses regression that happened several times in the past, see #27915 (closed)

Closes gitlab-org/quality/testcases#815 (closed)

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