This feature is Enterprise only (requires BUSL).
Serves GET/HEAD /vex/:version/vex.json for Talos ≥ 1.13.0.
Pulls exploitability data from an OCI registry, generates a VEX
document via go-vex, and caches it in-memory with configurable TTL.
Signed-off-by: Mateusz Urbanek <mateusz.urbanek@siderolabs.com>