Macos-pkg-builder

- Resolve packages embedding an empty pkg at `/`
- Regression from 2.0.0

- Implement new `FlatPackage` and `DistributionPackage` classes
- Intended for more advanced package configurations, including bundling multiple PKGs inside a single distribution package
- Implement more robust subprocess logging for errors
- Implement Copy on Write (COW) for package resources
- 20% faster package creation on average

- Expand distribution type package configuration:
- Pass MARKDOWN to configure welcome, readme and licensing in the package
- Pass light and dark mode images to configure the package background
- Pass title to configure the package title
- Header: `Install {title}`
- Welcome: `Welcome to the {title} Installer`
- Add additional FileNotFound error handling for missing resources
- Add support for passing README and LICENSE content to the package as markdown
- Configured via new `pkg_readme` and `pkg_license` parameters

- Fix project name typo in `setup.py`

- CI: Switch to `svenstaro/upload-release-actionv2`
- Resolve Munki erroring on payload-less packages
- Enforces `--root` parameter for `pkgbuild`
- Add support for pre/postflight scripts
- Configured via new `pkg_preflight_script` and `pkg_postflight_script` parameters
- Enforce stricter bin pathing for `cp` and `chmod`
- Avoids 3rd party tools from being used
- Publish project version via `__version__` attribute
- Convert project to a package

- Add support for signing distribution archive
- Resolve missing return statement in `_sign_pkg()`