Doing schema validation for safe-settings.

[decyjphr]

@jonathanmorley had raised a PR #689 to merge JSON schema for validating settings.yml. This is a great start! And @luvsaxena1, @zpratt, @primetheus, have also done various implementations of schema validation checks in their environments to catch errors in the settings yaml -- in the IDE or during the PR check.

I am new to this and I've been looking through the docs for Zod (Which Zach has been using) and AJV (Which I found via search).

I created this issue to allow us to collaborate and take their work and have some sort of schema validation in safe-settings.

[primetheus]

@decyjphr I looked at ajv, but I haven't seen zod. Ours is built using openapi-request-validator, but we're hitting an issue with the rulesets due to an issue with traversing $ref in the enforcement in @octokit/openapi schemas. I'm definitely interested in seeing how others are handling rulesets