feat(php): Generate project

[amckinney]

Overview

This sets up the PhpProject (which depends on the new AbstractProject also used by the CsharpProject). With this, we now have a lot of the core infra setup to:

1. Generate source files
2. Define as-is files copied directly into the project
3. Generate all the base project files (i.e. composer.json, phpunit.xml, phpstan.neon, etc).
4. Build, test, and lint all files in seed and in CI (via the generated .github/workflows/ci.yml).

Misc. notes

1. A simple Placeholder.php file is generated for now so that we demonstrate the full directory tree.
2. The TypeScript generator context was updated to include a version so that it could be consolidated on the AbstractGeneratorContext.
3. The namespace configuration option was added to both the model and SDK generators since this will be inevitably be required by a variety of users.

[amckinney]

Note that we're running all of the scripts defined in the generated composer.json file, so we'll know whenever anything is wrong with the generated code.

We do this in a single line to reduce the number of containers spun up.

[dcb6]

🚀