Draft a CEP for `conda` Plugins Standards and Best Practices

With all of the [upcoming plugins work](https://github.com/conda-incubator/ceps/pull/32) and the possibilities related to them, it would be beneficial to come up with a core set of standards and best practices that have been discussed and agreed upon.

Possible topics to discuss include:

- Versioning
- Terminology
- Tests
- Verbosity / debug output
- Output format
- Preserving certain `conda` CLI arguments (e.g., `-n`, `-p`, `-c`, etc.)

**Note:** Standards that would only apply to certain plugins (e.g., a solver or authentication plugin) may be discussed within a separate CEP for those particular plugins.