Centralized Per-Project Contributor files

[clintoncwolfe]

This is part of the 2025 Repository Standardization Initiative.

Since there is wide variance across the repos as to the contents of the CONTRIBUTING.md files, we decided:

• that each repo's CONTRIBUTING.md should simply contain a link to somewhere more authoritative
• that the authoritative copy of the contributing guide should be in one governance repo, chef-oss-practices, rather than in many different project repos (such as chef/chef, etc). Thus chef/chef will refer to chef-oss-practices.

Based on this, we will move the contents of each of the major projects' CONTRIBUTING into this repo, and replace the disparate copies with links to this repo.

Like all content in this governance repo, the policies contained in the documents are currently under review.