solana catchup doesn't work when a validator runs with --private-rpc

[mvines]

The solana-validator --private-rpc ... flag allows validators to hide their RPC port from the rest of the cluster while retaining it open for their private use. But this breaks the solana catchup command, which relies on finding the validator's RPC port in gossip.

For solana catchup to work in this configuration, --private-rpc users will need to tell solana catchup their RPC port. The best option I see for this right now is to Expand solana catchup <PUBKEY> to solana catchup <PUBKEY or RPC URL>:

$ solana catchup http://127.0.0.1:8899