Externalize i18n strings from blob/show.html.haml

What does this MR do?

Externalizes i18n strings from app/views/projects/blob/show.html.haml

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [n/a] Documentation (if required)
• Code review guidelines
• [n/a] Merge request performance guidelines
• Style guides
• [n/a] Database guides
• Separation of EE specific content