Put text viewer behind a feature flag
In #324326 (closed) we added a text viewer as part of the ongoing blob refactor.
Since then there has been a lot of discussions around whether we should render text files with monaco (currently refactored to use monaco), highlightjs, custom solution, or stick with Rogue (pre-refactor solution).
This issue suggests putting the current refactored text viewer (Monaco) behind a feature flag.
This will put us in a better position to enable the refactor feature without being dependent on having decided the best way forward regarding the text viewer.
Note: with this change, the idea is to render text files with the legacy (Rogue) text viewer when the feature flag is disabled.