We had a discussion about how folks should use the new app user and whether they should use its name or UID for the USER instruction. We decided that the UID is best since it works better with the runAsNonUser Kubernetes feature.

Plan:

• Add ENV APP_UID=64198 to runtime-deps layer
• Encourage users to use the following pattern: USER $APP_UID

It's possible that having an ENV for the UID may be useful for other scenarios.

Note: Check #4693 and #4715 for final plan.

@karolz-ms