Add appsettings bicep module so app settings are preserved upon deployment

[bbarber]

Pull Request Checklist

• Did you pull latest and merge develop (or master) into your branch?
• Did you add tests?
• Did you run the front-end tests (if applicable)?
• Did you run the back-end tests (if applicable)?
• Did you include screenshots or a demo video (if applicable)?
• Did you include a descriptive title and description with your PR?
• Did you perform a self-review before assigning reviewers?

Without this change - any manually added app setting would get destroyed. This will add new values / update existing values, but it will not delete existing items.