Refactor CLI and add more commands

[lorisleiva]

This PR leverages instruction plans in the CLI of the program metadata program to create complex operations in a simple API. It results in the following API:

Commands:
  write [options] <seed> <program> [file]   Create or update a metadata account for a given program.
  create [options] <seed> <program> [file]  Create a metadata account for a given program.
  update [options] <seed> <program> [file]  Update a metadata account for a given program.
  fetch [options] <seed> <program>          Fetch the content of a metadata account for a given program.
  set-authority [options] <seed> <program>  Set or update an additional authority on canonical metadata accounts.
  remove-authority <seed> <program>         Remove the additional authority on canonical metadata accounts.
  set-immutable [options] <seed> <program>  Make the metadata account immutable, preventing any further updates.
  close [options] <seed> <program>          Close metadata account and recover rent.
  create-buffer [options] [file]            Create a buffer account to use on metadata account later on.
  update-buffer [options] <buffer> [file]   Update an existing buffer account.
  list-buffers [authority]                  List all buffer accounts owned by an authority.
  fetch-buffer [options] <buffer>           Fetch the content of a buffer account.
  set-buffer-authority [options] <buffer>   Update the authority of an existing buffer account.
  close-buffer [options] <buffer>           Close an existing buffer account.