Move to changesets for release management

[benweatherman]

Apollo is adopting changesets across a lot of our projects and lerna was recently deprecated (though there's perhaps life left for lerna). Federation should likely follow the lead and start using changesets.

There's an example repo that could help guide us through the transition and apollo-utils is using it.

Some things to consider:

1. Will this allow us to bump versions in lockstep? Currently we bump all package versions together and will need to support that.
   • Yes, we would need to setup fixed packages
2. How do we make sure it's easy for contributions? We should make sure our docs on how to submit changes are accurate and up-to-date.

[benweatherman]

Note that implementing this would fix #1815 as well

[benweatherman]

Nice work @clenfest!