Added Blob Edit Header component

What does this MR do?

This MR is a small part of the effort of refactoring Snippet edit form to Vue. This particular one deals with adding just one component that renders Snippet blob's filename with reactive communication about its changes.

NOTE: This MR is part of a larger user-facing effort, hance no CHANGELOG entry has been provided for now.

Screenshots

	Before	After
With file name
Without file name

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

References #207240 (closed)