Automate version bump and package publishing for airbyte-cdk

[clnoll]

Tell us about the problem you're trying to solve

There are two issues when publishing the CDK:

1. Many people could be working on the CDK in parallel, which results in version conflicts between in-flight PRs for the airbyte-cdk package
2. Publishing the CDK is done from a branch, which can lead to nasty race conditions, not to mention being tedious/manual

Describe the solution you’d like

We could solve the two problems at once, or we could solve just one or the other.
To solve 1 we need to add a GitHub Action to bump the version and publish the package on merge to master. If we do this, we'll want a way to indicate whether it's a major/minor version change. One possible solution could be to use the commit message, or possibly the PR description since the template indicates whether there are breaking changes.

To solve 2 we need a Github action that checks whether the airbyte-cdk directory was changed on merge to master, and runs the publish workflow if so. We will also need a clear path for error recovery if the publishing fails for any reason.

The implementer of this issue is free to think about whether to solve both issues vs. just one, and the sequencing of a solution.

Describe the alternative you’ve considered or used

We could queue up the PRs that would require a version bump and merge them once a day. We might end up wanting to do this eventually anyway, with or without automatically bumping the version, so it's somewhat orthogonal.