Publish an RFC book

[adpaco-aws]

Publish an RFC book using mdBook. Hopefully, an RFC book will make it easier for Cedar contributors and others to access the most up-to-date version of accepted RFCs, summaries of RFC statuses, and also act as an alternative to GitHub's Markdown rendering.

The changes in this PR are mainly:

• Adding/moving files around to get mdBook to work as smoothly as possible.
• Adding a new workflow to deploy the generated content to GitHub Pages.

I've tested these changes in my own fork, and the results can be accessed here: https://adpaco-aws.github.io/rfcs/

Rendered

[mwhicks1]

This looks great! But: Should RFC 68 be dropped? It was superseded by RFC 82. Should probably "un-accept" it in this repository along with changing the mdBook to not include it.

[adpaco-aws]

Good point, I've changed the SUMMARY.md file to not include RFC 68.

I don't think we've actually defined what the process to "un-accept" an RFC is, but we have at least two options:

• If we want to keep the latest version of RFC 68 for historical reasons, we could include it in the archive folder that Reform the RFC process #90 introduces.
• Otherwise, we should just delete it. Note that RFC 82 refers to the PR (this) and not the RFC file, so this can already be done.

[mwhicks1]

we could include it in the archive folder

I like the idea of doing this. It was accepted, and has useful context/discussion compared to the 82.

[shaobo-he-aws]

LGTM.