TLS Credentials in gRPC Probe

The new gRPC health probe enables developers to probe gRPC health servers from the node. This allows them to stop using workarounds such as this grpc-health-probe paired with exec probes. It allows natively running health checks on gRPC services without deploying additional binaries as well as other benefits outlined in the announcement. A limitation in the current implementation is that it only supports gRPC servers that do not leverage TLS connections. Even if they are not concerned about certificate verification for the health check, a connection cannot be established at all if the server is expecting TLS and the client is not. This enhancement aims to add configuration options to enable TLS on the gRPC probe.