As part of the charter of CDK v2 no longer having any breaking changes, the RFC(s) related to experimental APIs defined a convention of suffixing APIs which are known to be experimental.

The general idea is that new API elements which are experimental in nature and likely to change should be suffixed with something (e.g., BetaN) to denote the preview nature of them, and as breaking changes are needed, the suffix will be incremented. This applies to classes, methods, and members.

This task is to update the CONTRIBUTING and DESIGN_GUIDELINES docs with the updated guidance. The implication as well is that the PRs to update these documents will concretely solidify the guidance, in terms of the actual suffix and scheme.

More context:
https://github.com/aws/aws-cdk-rfcs/blob/master/text/0249-v2-experiments.md#release-notes
aws/aws-cdk-rfcs#377 (comment)
#13780 (comment)
https://github.com/aws/aws-cdk-rfcs/blob/master/text/0249-v2-experiments.expired.md#option-6-api-previews