Feature Request: `vm` commands for Composer, PHP, and WP-CLI

### Summary

Add `trellis vm` commands that utilize `trellis vm shell --workdir=<cwd> <command>` for: `composer`, `php`, and `wp`

This would allow for more quickly executing Composer, PHP, and WP-CLI commands

Examples:

```shell
$ trellis vm composer install
$ trellis vm wp acorn optimize:clear
$ trellis vm php script.php
```
