Bug fix: Install packages into working directory

[sophiewigmore]

Summary

#46

• Rolls back changes made in Run autoloading separately from composer install #25 and instead installs all packages into /workspace/vendor directly. This is done to prevent symlinking issues with composer, in which packages installed into the layer cannot find files in /workspace like .env and classes outside of vendor.
• The /workspace/vendor directory is manually copied into a layer for caching
• This enables framework support which previously failed to build due to symlinking issues
• Tests added for:
  • Laravel app
  • Symfony app
  • Drupal app (removed because it was enormous, and was previously failing for the same symlinking issues as the other two apps)

#90

• Fixes vendored app rebuilds
• When performing a rebuild of a vendored application, the app /workspace/vendor dir is cleared and the cached vendor directory from the layer is copied into /workspace.

Open questions:

• can we optimize the code to avoid copying vendor to layer
• how could we instead leverage slice layers rather than copying around vendor?

Use Cases

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).

[sophiewigmore]

The tests are passing locally :/ investigating

[thitch97]

This all looks good to me! Just had one question