Enhance and Simplify App Settings

[jbouder]

The current setup pushes the use of a .env for managing env variables, which can be confusing and doesn't scale well. In order to simplify this, the config should be updated with default values as well as optional values where possible.

Description

• Updated app settings with default DATABASE_URL
• Updated app settings to make OIDC_CONFIG_URL optional
• Updated Readme to make .env optional and only needed for local overrides
• Updated Dockerfile to remove explicit copy of .env
• Updated workflow to remove vars as no longer needed

Related Issue

N/A

Motivation and Context

• Simplifies the process of getting up and running
• Better supports CI/CD automation where environment variables are more likely to be set in a pipeline

How Has This Been Tested?

• Local Testing

Screenshots (if appropriate):

[marshyski]

LGTM