Add EXPERIMENTAL disclaimer to specific arguments and command

[endersonmaia]

Context

We should be explicit which commands and arguments are experimental in the cli docs and output.

Some features that are being integrated into cartesi/cli v2 are:

• coprocessor command
• espresso-reader integration

Considering those initiatives are still experimental in the official docs point of view, we should also align the cartesi/cli.

Proposal

Add a EXPERIMENTAL text for commands and arguments that are considered exprimental.

Ex,:

cartesi --help
Usage: cartesi [options] [command]

Options:
  -V, --version            output the version number
  -h, --help               display help for command

Commands:
  coprocessor [options] EXPERIMENTAL
...

CHANGELOG should also be updated to inform which feature is experimental, and remove this disclaimer when it's considered official support.