Consider AAD Client ID env variable as a build error versus a runtime error

[rickrain]

Copied from Azure Dev Ops Backlog

Currently, the user can optionally pass in the WEBPACK_PROP_AAD_CLIENT_ID env variable. The app will build and run without error. When the user tries to login the app will throw an error if this is not set. This improves the dev experience because if the dev is not working on a feature within the auth pipeline then they don't need to worry about this env var. However, if the project was deployed without this env variable then the user would experience this error and it would have to be fixed by the project developers.

There are user & developer experiences to consider with how to handle this.

Should we throw a build error (or warning) if it is not passed in? Should we improve the UI design to reflect if auth has been configured or not. etc...