Move website_docs back to website repo

[chalin]

Originally posted by @arielvalentin in #1394 (comment)

... I am in favor of moving the docs! My one request is that @open-telemetry/ruby-approvers and @open-telemetry/ruby-contrib-approvers be granted collaborator access and added to CODEOWNERS to the ruby docs in repo so that we are able to approve PRs.

Contributes to open-telemetry/opentelemetry.io#730. Tasks (in order):

• Wait for Add API ref and Examples to docs sidebar #1394 to be merged
• In website repo, perform the tasks detailed in Migrate Ruby docs to this repo opentelemetry.io#1942
• Delete website_docs from this repo - Delete website_docs directory #1402

/cc @cartermp

[cartermp]

Everything's done on the website side of things! open-telemetry/opentelemetry.io#1942