Add end to end decode examples

It'd be great if we had a couple of example binaries in this folder which use the absolute minimum of code to decode a specific block or storage entry from an RPC node.

Perhaps we'll end up with two separate commands/binaries like:

• decode_storage --block 1234 --pallet System --entry Accounts --types types/polkadot_types.yaml --url wss://rpc.polkadot.io
• decode_block --block 1234 --types types/polkadot_types.yaml --url wss://rpc.polkadot.io

These commands wouldn't do anything clever or have great error handling or whatever; just print basic information on decoding. To see the required logic we can look at the more complicated subcommands in https://github.com/jsdw/polkadot-historic-decoding-example/tree/main/src/commands.

Start by reviewing the existing example binaries in this folder and the more complicated subcommands in polkadot-historic-decoding-example/src/commands. Trace the minimum logic needed to connect to the RPC node and decode a block or storage entry using the supplied types file. Done means two commands accept the proposed arguments and print basic decoded information.