Resume development of CLI-related high priority features and improvements

[cpatsonakis]

This issue is essentially a continuation of #477 and is solely focused on developments regarding the CLI, following the recent update of the repository's structure.

The following already implemented changes will be introduced in the respective branch:

• Allow jwk_jcs_pub option to be specified for newly created did:key.
• Expand VC verification policies set to additionally include: allowed-issuer, webhook and revoked_status_list.

Additional items that require development:

• Introduce vp root command with create and verify subcommands.
• Extend and improve overall documentation organization.

And of course, test cases all around 😄