Saving an annotation will trigger a save to S3 when snippetKey is presetn

[solkaz]

Description

This PR refactors the handleSaveAnnotation method of the Annotation container component to add a check for the snippetKey prop. If it is non-empty, then an action will be dispatched to save the snippet state to S3. If it is empty (i.e. the snippet hasn't been saved yet) then the action to save to S3 won't be dispatched.

Motivation and Context

Fixes #373

Checklist:

• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

Screenshots (if appropriate):