podman-etcd: compute dynamic revision bump from maxRaftIndex (#2087)

Replace hardcoded 1 billion revision bump with dynamic calculation based
on 20% of the last known maxRaftIndex from revision.json.

This aligns with the logic used by cluster-etcd-operator's
quorum-restore-pod utility and ensures the bump amount is proportional
to the cluster's actual revision state.

The implementation:

• Adds compute_bump_revision() function with safe fallback to 1bn default
• Extracts magic values to named constants (ETCD_REVISION_BUMP_PERCENTAGE, ETCD_BUMP_REV_DEFAULT, ETCD_REVISION_JSON)
• Validates computed values (non-zero, not exceeding default)
• Logs computation results for debugging

Reference:
https://github.com/openshift/cluster-etcd-operator/blob/215998939f5223da9166
22c71fd07d17656faf6b/bindata/etcd/quorum-restore-pod.yaml#L26-L34