Provide a Simple and Native Certificate Management Solution

[danehans]

While https://github.com/envoyproxy/gateway/issues/81 identifies the need for a production-quality certificate management solution, EG should support native cert management for simple, non-prod use cases.

[robd003]

I'd suggest looking at lego

[danehans]

I'm closing this issue since a simple self-signed CA-based solution was implemented in https://github.com/envoyproxy/gateway/pull/208. A more comprehensive solution will be implemented to resolve https://github.com/envoyproxy/gateway/issues/81.