Consider a lightweight RFC process for the SPIRE project

[evan2645]

Many OSS projects have RFC processes of sorts which are exercised when adding new features or otherwise making non-trivial design decisions. As the SPIRE project grows, more ideas are proposed, and additional maintainers and contributors are brought on board, it is important to ensure a consistent vision and community agreement.

Some research should be done on existing RFC processes on OSS projects, and we should evaluate them for adoption in the SPIRE project. The CNCF, and other more mature projects hosted by it, could help to serve as a guiding light.