refine error message caused by internal kafka failures

[neverchanje]

Though this is indeed an internal error, the message is quite unfriendly to read. The error is user-facing. We should refine it and let users immediately know the cause and how to fix.

dev=> create materialized view ad_mv as select * from ad_source;
ERROR:  RPC error: GrpcStatus(Status { code: Internal, message: "internal error: Meta data fetch error: BrokerTransportFailure (Local: Broker transport failure)", metadata: MetadataMap { headers: {"content-type": "application/grpc", "risingwave-error-bin": "CAESX2ludGVybmFsIGVycm9yOiBNZXRhIGRhdGEgZmV0Y2ggZXJyb3I6IEJyb2tlclRyYW5zcG9ydEZhaWx1cmUgKExvY2FsOiBCcm9rZXIgdHJhbnNwb3J0IGZhaWx1cmUp", "date": "Thu, 23 Jun 2022 05:48:12 GMT", "content-length": "0"} }, source: None })

Internal Error: The connection to Kafka brokers ("127.0.0.1:29092") is broken, please check its availability.

[neverchanje]

fixed by #4227