Add gRPC keepalive settings to maintain stable connections between
woodpecker-agent and woodpecker-server:
- WOODPECKER_GRPC_KEEPALIVE_TIME=10s: Send ping every 10s to detect
stale connections before they timeout
- WOODPECKER_GRPC_KEEPALIVE_TIMEOUT=20s: Allow 20s for ping response
before marking connection dead
- WOODPECKER_GRPC_KEEPALIVE_PERMIT_WITHOUT_CALLS=true: Keep connection
alive even during idle periods between workflows
Also reduce Nomad healthcheck interval from 15s to 10s for faster
detection of agent failures.
These settings address the "queue: task canceled" and "wait(): code:
Unknown" gRPC errors that were causing step logs to be truncated when
the agent-server connection dropped mid-stream.