Add a way for a client to specify operation datastore

[sydhds]

Intro

In massa-client, there is currently no way to specify an operation datastore when using the command read_only_smart_contract.

Todo

• [ ] Find a way to specify key / value (or the entire datastore)
  • [ ] Maybe in 2 ways: by key: value one by one or via a file (but which format?)
• [ ] Implement this in massa-client, file cmds.rs

[damip]

This applies to the following commands from the client:

• read-only executions
• sending ExecuteSC operations

[damip]

I think this will be limited to API access, because allowing the user to specify binary stuff in the REPL is not practical