CI flow tooling

[alexkli]

Provide tooling/examples/documentation to use edgly in a CI flow:

• automatically create fiddles from new branches/PRs and link to fiddle in PR comment
• some way to pull in fiddle changes back into PR, e.g. via checkbox click in the PR comment (but ensure only users with write access to code can do this)
• deploy to stage and run tests on PR commits
• deploy to prod and run tests on main commits
• regularly run prod tests via CI as health monitoring