docs: RPC endpoints linked from docker page do not have both RPC and gRPC

[jcstein]

from @smuu

In point 3 it talks about RPC endpoints, but we need an endpoint that has RPC and gRPC. Also, the mainnet link is correct, but the Mocha and Arabica links should also link to sections where endpoints with both ports are listed.

for this issue, there are no existing sections on mocha/arabica where endpoints with both ports are listed

[jcstein]

notes:

• check if ports 26657 (RPC) and 9090 (gRPC) is open
• If you want to validate the endpoints
  • use curl against the RPC endpoint to get e.g. current height (path /status?)
  • use grpcurl against the gRPC endpoint to see if it lists all available requests