Kadena LC prepending http for proof-server

[rsoeldner]

Running
MODE=SNARK RUST_LOG="debug" cargo run -p kadena-lc --release --bin client -- -c https://api.chainweb.com -p http://?????:6379

results in an error message:

Failed to initialize light client: Request for endpoint "http://http://????.com:6379/longest-chain/proof" failed: error sending request for url (http://http//????.com:6379/longest-chain/proof)

Either, the format of the proof server has to be documented or should construct the url correctly.

Being created here: https://github.com/argumentcomputer/zk-light-clients/blob/dev/kadena/light-client/src/client/proof_server.rs#L73