`phylum extension` subcommand installation management

[andreaphylum]

Overview

The user should be able to add, remove and list extensions via the appropriate phylum extension subcommand.

Acceptance Criteria

• When a user runs phylum extension add . the extension in the current working directory should be installed.
• After a user installs a new extension, foobar, it should become available to the user under the phylum cli, e.g., running phylum foobar should execute the foobar extension.
• When a user installs a valid extension it should print a message indicating success. It should also print a quick guide on the extension to give the user some context on how the given extension works.
• When a user attempts to install an invalid extension, it should fail and inform the user as to why.
• When a user runs phylum extension remove <extensionName> the extension should be entirely removed from the user system.
• When a user runs phylum extension or phylum extension list a list of currently installed extensions, their versions and a short one sentence blurb on what the extension does should be shown in a table format.

Associated User Story

https://www.notion.so/phylum/Extension-Base-CLI-Capability-bff6fcf7c0c947b79b8c49a928f59cc4