Add changesets

[benweatherman]

Followed examples from Apollo's own @apollographql/typescript-repo-template and straight from the changesets docs

• Updated RELEASING.md to reflect the move to changesets
• Updated CONTRIBUTING.md to be more succinct and hopefully more helpful
• Removed DEVELOPMENT.md since it's all about how to do the previous incarnation of publishing
• Removed lerna stuff

Fixes #1846

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