Add a GitHub Action for synchronizing snippet updates

[patrick-fs]

Use case

• The "source of truth" snippet is updated and exposed via the FullStory /code/v1/snippet endpoint
• A GitHub Action on this repository polls this endpoint for changes every 24 hours
• If changes are detected, a new PR is created and assigned to the folks in MAINTAINERS.json

3 scenarios

(Using the GitHub Action results from my fork: https://github.com/patrick-fs/fullstory-browser-sdk)

Review the output of the Sync snippet step:

• Remote snippet changes are captured in a new PR
• An open PR for snippet synchronization causes the GH Action to fail
• No changes