Update Dockerfile to run Java 17

[jakob-p]

The latest Version of the diga-api-client 2.0.0-beta.1 will break when validating or billing codes other then the test code because the dependency update of base32check-java to 0.1.0 requires Java 17.

This PR updates the production docker image to use Java 17. It uses the eclipse-temurin:17-alpine image to have a more lightweight docker image. It also adds a new user in order to avoid running the application as root.

• Upgrade production docker image to use Java 17 to make the build compatible with the latest diga-api-client

• in the production docker image create a new user so the application is not run as root

[gtuk]

@jakob-p thanks for your contribution. Your changes together with the changes from https://github.com/gtuk/diga-api-service/pull/25 are now released as version v2.0.0 https://github.com/gtuk/diga-api-service/releases/tag/v2.0.0