Made faster external loading optional and disabled by default as it w… (#1865)

* Made faster external loading optional and disabled by default as it was causing bugs, added experimental option to disable libredirect to improve performance

* Add per-container toggles: opt-in external-storage fastpath, disable libredirect (minimal W^X-only shim on modern)

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Co-authored-by: Utkarsh Dalal <utkarsh.dalal@toptal.com>