Add changesets to create changelogs

[roninjin10]

Description

Since mocktimism will initially be released in alpha and subject to breaking changes it is important that changlogs be kept for the npm and go packages. By using changesets with the github plugin release notes will be created in this github and the npm releases

https://github.com/changesets/changesets

Tasks

• [ ] Add changesets folder https://github.com/ethereum-optimism/optimism/tree/develop/.changeset
• [ ] Add appropriate release version and changeset scripts to package.json https://github.com/ethereum-optimism/optimism/blob/develop/package.json#L30
• [ ] Add github action for releasing https://github.com/ethereum-optimism/optimism/blob/develop/.github/workflows/release.yml
• [ ] Add github action for releasing snapshots https://github.com/ethereum-optimism/optimism/blob/develop/.github/workflows/release-snapshot.yml

[roninjin10]

Not needed