[POR-655] Environment settings handler and option to set specific git branches to trigger preview env

[mnafees]

Pull request type

Please check the type of change your PR introduces:

• [ ] Bugfix
• [ ] Feature
• [x] Other (please describe): Improvement

Pull request checklist

Please check if your PR fulfills the following requirements:

• [x] If it's a backend change, tests for the changes have been added and go test ./... runs successfully from the root folder.
• [ ] If it's a frontend change, Prettier has been run
• [ ] Docs have been reviewed and added / updated if needed

What is the current behavior?

Right now we only have the option to toggle new comments on a PR.

What is the new behavior?

This PR introduces the concept of settings for an environment. We already have the setting to disable new comments for an environment (git repository). We now introduce the choice of specific git repo branches that the preview env should be making deployments for.

Technical Spec/Implementation Notes