Create CLI

[webbertakken]

We'd like to create a CLI so that the action can use it instead of having its own logic.

Later this CLI would move to its own repository.

The CLI can later be used from all CI environments as well as locally.

Scope:

• Includes general architecture
• Does not include any builder functionality

AC:

• Being able to work locally, so that we can start adding functionality.

[webbertakken]

Probably it's a good idea to first fully convert builder to Deno and then start with the CLI.

If nobody disagrees then game-ci/unity-builder#413 becomes a pre-requisite for this issue.