Proposal #108: Update DevShard v5 to v5.0.2

Update DevShard v5 to v5.0.2 and retire v3 and v4 This proposal is a critical fix for the overall Devshard deployment. Each running Devshard version opened a Postgres pool sized to the host CPU count. Several versions on one multicore host used every connection and the node failed. It removes the outdated v3 and v4 binaries, leaves v4.1 unchanged, and updates v5 to v5.0.2. v5.0.2 caps payload pools at the session limit (PG POOL MAX CONNS, default 4). It also stops inference-timeout waits from stacking a timer on every heartbeat, opens the next heartbeat one interval after turnover, and records which process holds a validation lease so only that process can finish or release it. No bounty. Pull request: https://github.com/gonka-ai/gonka/pull/1840 The description: https://github.com/gonka-ai/gonka/blob/devshard-0.2.x-v5.0.2/proposals/governance-artifacts/update-v0.2.15-devshard-v5.0.2/README.md (sha256 fed37d85d55fd9625189d24704baa8a58904c7525c4fa23edc63d673abd4c81b)