Add support for GitHub workflow usage without pull requests

[ebickle]

The example at https://github.com/snyk-playground/config-repo/blob/main/.github/workflows/perform-import.yml shows how to use a GitHub workflow to run the snyk-sync tool. To store it's cache, it requires continual commits (via Pull Requests) back to the repository.

Instead, using the official actions/cache GitHub action could allow the sync to work using native GitHub workflow caching. Ideally, the "sync" or "config" repository shouldn't ever require commits for regular operation - perhaps with an update to the example workflow and some code adjustments this would be possible?