Provide an easy way to bundle up changes to projects

[soenkehahn]

For example I would like to be able to provide a library (or helper function in the garn ts library) that:

1. calls .addCheck("prettier-check", "prettier --check *.ts"), and
2. calls .addExecutable("prettier", "prettier --write *.ts")

on a given project.

One way of using such a helper I could imagine is this

export const myProject = garn.mkNpmProject(...).add(garn.javascript.prettier())

What probably should also be allowed is:

export const myProject = garn.mkNpmProject(...).add(garn.javascript.prettier("*.ts"))