Add support for buildpack.toml manifest

[pombredanne]

This is a package manifest format for Heroku and Packeto:
See https://github.com/search?q=path%3A**%2Fbuildpack.toml&type=code&ref=advsearch

Adding support would consist in:

1. Research and document here as comment the buildpack format specification and various spec versions
2. Collect a few representative test files and attach as comment keeping track of the URL provenance for each
3. Create a new packagedcode/buildpack.py module with an overall structure similar to that of existing modules. Implement parsing and creating a Package.
4. Add tests in a new test_buildpack.py test module using the collect test files
5. Add extra unit tests for single functions

[hp77-creator]

Hey @pombredanne , Looks good issue, I would like to learn more about it and maybe contribute to it, Shall I work on it If there's no one else working on the same?

[arshad-muhammad]

@pombredanne I'm interested in extending the project to handle the buildpack.toml manifest and wanted to check in to ensure I understand the full scope of the task.

Could you please provide a bit more context regarding:
The specific parts of the project that need this support?
Any particular edge cases or functionality you'd like to be considered?
How you envision the buildpack.toml information being utilized in the system (e.g., dependency handling, build steps)?

[NucleonGodX]

Hello @pombredanne This is my analysis, I've opened a pull request trying to implement it, kindly review it when you have time.

1. https://buildpacks.io/docs/reference/config/buildpack-config/
   This is the format spec for buildpack files

2. few test files used:

For Paketo buildpacks-
https://github.com/paketo-buildpacks/dotnet-execute/blob/main/buildpack.toml
https://github.com/paketo-buildpacks/git/blob/main/buildpack.toml
https://github.com/paketo-buildpacks/java-memory-assistant/blob/main/buildpack.toml
https://github.com/paketo-buildpacks/opentelemetry/blob/main/buildpack.toml
https://github.com/paketo-buildpacks/pipeline-builder-canary/blob/main/buildpack.toml

For heroku buildpacks-
https://github.com/heroku/heroku-buildpack-php/blob/main/buildpack.toml
https://github.com/heroku/heroku-buildpack-java/blob/main/buildpack.toml

[AyanSinhaMahapatra]

@NucleonGodX see PR for comments