Allow existing Defender configurations to be imported for SSOT

[cylon56]

Currently the serverless plugin is basically a one-way road for deploying configurations. Defender configurations are defined in serverless.yml that can be easily deployed with the possibility of also rolling things back if SSOT mode is true.

However, some users might make changes from the Defender UI or have an existing setup that they'd like to start from. Currently, SSOT mode would remove any existing or modified instances that aren't already defined in the repo. It would be nice to be able to import changes into the repo.

Its possible to create a way for existing Defender configurations to be pulled from a Defender instance via GitHub Actions or a local script that then applies those config changes to the git repository. This could be done through an auto-generated pull request that provides developers the opportunity resolve any merge conflicts.