Add command for updating existing WP packages

[mikeybinns]

We currently have a script in LP projects for updating WP packages, but it's custom to each use case because different packages are used.

We would benefit from a single command which updated all @WordPress namespaced packages present in package.json as they all have the same tag system.

[mikeybinns]

This is on hold, Wordpress removed the tagging system from their packages, so we can't use them for this tool anymore. Will open a new issue if and when this is possible.