Draft: Rename edit_blob_header for snippets to snippet_blob_edit_header

What does this MR do and why?

while reviewing !205529 (merged), i noticed we got app/assets/javascripts/repository/pages/blob_edit_header.vue and app/assets/javascripts/blob/components/blob_edit_header.vue :scream_into_pillow: i don't do well when two files have the same name in two different folders (neither does rubymine). so i updated one of them and moved it to the proper location.

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

editing snippets work as before

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.