Cli manifest command

[pileks]

Closes #1146

This PR introduces the manifest command and subcommands into the Polywrap CLI.

Commands:

polywrap manifest migrate migrates your current project manifest to the latest version.
polywrap manifest migrate build migrates your build manifest to the latest version, same goes for all other extension manifests.

polywrap manifest schema prints out a YAML-ish schema for your current project manifest.
polywrap manifest schema build does the same, but for your build manifest, etc.
The schema command auto-detects your current manifest format, or just outputs the latest version if no manifest file is found.