Proposal: Criteria for community contributions

# [Proposal] Criteria for community contributions

Related to:
- https://github.com/devcontainers/spec/issues/71
- https://github.com/devcontainers/spec/issues/58
- https://github.com/devcontainers/devcontainers.github.io/issues/244
- https://github.com/orgs/devcontainers/discussions/86

## Goal

As our set of community-contributed Features and Templates continues to grow, we should establish a set of criteria so that it's easier for:
* The community to include any and all required info in a contributing PR
* The spec maintainers to review contributions
* Dev container users to select the right resources

## Proposal

### User contributions
A proposed Feature or Template contribution to our [community index](https://github.com/devcontainers/devcontainers.github.io/blob/gh-pages/_data/collection-index.yml) should include the following:
- Clear readme and PR description, including:
- Owner / maintainer, including if they're part of a verified org
- Usage scenario
- Any dependencies and pre-reqs (i.e. required OS or platform)
- Fully functional code that is clearly new / distinct from an existing Feature or Template
- We shouldn't have Features or Templates that clearly repeat functionality defined in existing items in the index

### Spec changes
We'll want to consider a few changes into the specification to support this process:
- Pull request templates on GitHub
- We should consider creating PR templates on GitHub in the [Features](https://github.com/devcontainers/features) and [Templates](https://github.com/devcontainers/templates) repos that list the required information listed above, so that it's easier for contributors to see what they should include
- https://github.com/devcontainers/devcontainers.github.io/issues/244 is a great option
- Publisher verification
- We can consider a publisher verified if they're verified on GitHub
- We need the ability to surface this on [containers.dev](https://containers.dev/collections) and in tooling
- Ability to declare where things work (i.e. OS or platform) https://github.com/devcontainers/spec/issues/58
- Filtering and sorting
- Related to the above, users should then be able to filter and sort containers.dev and tooling on several factors:
- Verified publishers
- Feature or Template usage (could start with surfacing stars the repo has received on GitHub)
- Where things work
- Private marketplace https://github.com/devcontainers/spec/issues/71
- In the case a company doesn't want to contribute their resources to our community index, or they don't fit the criteria outlined above, it'd be helpful for supporting tools to be able to allow users to include their own marketplace endpoint