feat: Add tcomposer command

[musaabhasan]

Description

Adds a tcomposer helper command as a shorthand for running Composer through the PHP container.

The command delegates to tphp composer ..., with tcomposer debug ... delegating to tphp debug composer ... for the debug PHP container.

Fixes #375.

Testing Instructions

1. Check out this pull request.
2. Run tcomposer install and verify it runs Composer in the default PHP container.
3. Run tcomposer debug install and verify it runs Composer in the debug PHP container.

Checklist

• Does what the author says it will do
• Testing instructions are provided
• Commit messages make sense and follow the conventional commit standard
• No identified security issues
• No identified maintenance issues
• Any third-party libraries/dependencies use the MIT or Apache 2.0 license
• Changes made are backwards compatible and will not break existing setups
• Changes to scripts in the bin/ directory run correctly on both MacOS and WSL
• Changes to containers can be built locally sucessfully (e.g. via tbuild container && tup container)
• Containers/images are compatible with both AMD64 (Windows) and ARM64 (MacOS)
• Changes made to config.php are compatible with our oldest supported Totara version, our newest Totara version, and Moodle

Local verification:

• git diff --check
• bash -n bin/tcomposer