swh-graph Add java process port monitoring

swh-graph is now based on a grpc process and a java process.

For some reasons (to determine) the java process can crash and let the grpc part alone without monitoring notification

We should be notified by the monitoring if nothing is listening on the port 50091

(we should also think to use a port outside the ephemeral range as nothing can guaranty the port is free when the service starts)

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Migrated from T4471 (view on Phabricator)