Add gh action to automate creation of changelog

[devisscher]

This PR adds a GH action, which checks for changesets when a new PR is created, then creates another PR that keeps track of changesets between versions.

We will follow a similar patter to Polaris, except this is a single package repo. So we won't need to differentiate releases for different packages.

This action for Changesets creates a pull request with all of the package versions updated and changelogs updated and when there are new changesets on your configured baseBranch, the PR will be updated. When you're ready, you can merge the pull request and you can either publish the packages to npm manually or setup the action to do it for you.

Once this is merged, we can move forward to automating the package release and possibly sending a slack message to a channel to alert of new versions 😄

[carrotderek]

Haha what's this file for?

[devisscher]

When creating a PR, we'd ask the contributor to create a change-set, explaining what they added to the code. If however, you want to create a PR which contains no changes worthy of a bump in version, you can use an empty change set to get CI passing.

Once this is merged, subsequent PR's will be checked for changesets, which will then update the "Version PR" that will be keeping track of changesets and updating the changelog. (This PR wouldn't be part of the changelog, because the changeset is empty)

[devisscher]

You can also use 🤖Skip Changelog to skip the check.

[carrotderek]

Changes looks good to me!