Enable :refactor_blob_viewer feature flag by default

What does this MR do and why?

The refactor_blob_viewer feature flag is currently globally enabled.

This enables refactor_blob_viewer by default.

Screenshots or screen recordings

N/A

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #324351 (closed)