Add an xb-dev-extras command

[TravisCarden]

This command performs some common setup tasks developers use when re/installing an Experience Builder environment:

$ ddev xb-dev-extras --dry-run
This command will...
  1. Install the following modules:
     - Admin Toolbar (admin_toolbar)
     - Admin Toolbar (admin_toolbar_tools)
     - Coffee (coffee)
     - "All-Props" Test SDC (sdc_test_all_props)
  2. Create a test page at '/test'.

It can be run on a fresh or existing environment, as long as ddev xb-setup has already been run.