generic cli client for node and worker interaction

[brenzi]

currently, the client performs a hard-coded example sequence. This task aims at a generic cli client with the following capabilities:

chain interaction:

• chain new-account -> generate new sr25519 key and store it in the keystore
• chain list-workers -> all workers listed with columns: ss58(account) | MRENCLAVE | RA timestamp | url
• chain list-shards -> all shards listed with the latest worker that commited a state update. colums |ss58(account)|latestIpfsHash
• chain transfer <from> <to> <amount> (public accounts)
• chain balance <account> (public account)
• chain listen -> listen to events and list all execution confirmations with their specifics

needs --node-url and --node-port

bridging (M6)

• shield <from> <to> <amount> <shard> -> send funds from public to private account (chain-to-stf)
• unshield <from> <to> <amount> <shard> -> send funds from private to public account (stf-to-chain)

worker interaction (stf-specific)

• stf new-account -> new private account, new sr25519 key and store it in private keystore
• stf transfer <from> <to> <amount>
• stf balance <me> -> must be in the p-keystore

getters need --worker-url and --worker-port

We should use clap_nested and define stf commands within the stf crate. Like this, the cli stays generic with respect to stf.

[brenzi]

@clangenb , @electronix please review cli suggestion. What more do we need?

[brenzi]

work started on branch brenzi_client