Update build_and_push.py to work with vite

The current version of osmybiz running on the staging server does not contain the oauth config it needs. build_and_push.py uses gitlabs CI/CD configuration and sets them as environment variables for the build.

This MR updates the script with the new names for the variables. Rather than setting them as "process environment variables" it now creates a .env.production file, as it seems simpler and prevents having to switch between import.meta.env and process.env depending on the "mode"

TODO: The gitlab secrets probably need to be updated (and perhaps named accordingly). I will have a look at this with Joël.