Specify settings in appsettings.json files instead of Kubernetes config

Currently, most settings are configured as environment variables in the Kubernetes deployment configuration. These settings should be defined in the appropriate appsettings.json file based on the environment (connection strings, logging, engines, etc.). Only secrets should be configured in by environment variables.

By default, ASP.NET Core supports three environments: Production, Staging, and Development. appsettings.json is for production and contains the defaults for the other files. appsettings.Staging.json is for QA. We could use it for external QA. appsettings.Development.json is for development. We will probably need to add another environment for internal QA, if it has different settings than external QA. We can call it InternalStaging or something like that, so that would use appsettings.InternalStaging.json.

Review the Kubernetes deployment configuration and the appsettings.json, appsettings.Staging.json, and appsettings.Development.json files described in the issue. Inventory non-secret environment variables and map them to the appropriate environment configuration, leaving secrets as environment variables. Confirm the ASP.NET Core environments and verify deployments still load the intended settings.