Add kzgpad util for using grpcurl to test eigenda

[teddyknox]

Why are these changes needed?

4844 encoding validation breaks naive grpcurl commands. This new CLI command can be used in combination with grpcurl to properly encode inputs, e.g.

grpcurl -proto ./api/proto/disperser/disperser.proto -import-path ./api/proto -d '{"data": "'$(tools/kzgpad/bin/kzgpad -e hello)'"}' disperser-holesky.eigenda.xyz:443 disperser.Disperser/DisperseBlob

Testing

I've tested this like this:

$ echo "hello" | go run tools/encoding-cli/cmd/main.go -e - | go run tools/encoding-cli/cmd/main.go -d -
hello

[jianoaix]

Thanks for making it easier for users to send requests

[ian-shim]

are the submodule changes intended?

[teddyknox]

@ian-shim nope... updated.