[WIP] Build viable Docker images for Polaris using Quarkus

[adutra]

⚠️ Not ready for review yet!

Requires #469, #604 and #628.

This PR redesigns how Docker images are built, to make them fully compatible with Quarkus.

• The main Dockerfile for Polaris server is now located at quarkus/server/src/main/docker/Dockerfile.jvm (default location for dockerfiles for Quarkus)
• The docker file can be built during the regular build: ./gradlew :polaris-quarkus-server:assemble -Dquarkus.container-image.build=true
• The images are built with the Quarkus docker build provider.

This PR modifies the eclipse-link module and includes 2 JDBC drivers in the resulting artifacts: H2 and Postgres. This is absolutely required to be able to run Polaris with Postgres as the JDBC drivers must be present at build time.

Test changes:

• For Helm tests, an image is built with Gradle and Quarkus, then loaded into minikube, with a custom tag. Then the tests are executed.
• For regression tests, an image is built with Gradle and Quarkus, then a regtests/docker-compose.override.yml file is created with that tag. Then the tests are executed.

This PR also fixes the issues described in #537:

• Removes the Dockerfile at the root of the repository (not needed anymore, and has security flaws);
• The docker-compose.yaml at the root of the repository is moved to the regtests folder where it naturally belongs.
• The default image in the docker-compose.yaml is apache/polaris:latest, meaning that by default, the regression tests execute against the latest released version of Polaris.
  • Note: there is no released version of Polaris yet, so running the docker compose file today will result in an error, unless the user builds the image manually; but that's a temporary issue.

This PR does not address the specific needs of release builds. For such builds, we need:

• Multi-platform manifests
• Various flavours of Eclipse Link dependencies (at least for now)
• (Probably) multi-registry pushes

Again, this PR also defers all documentation changes to a follow-up task.

And last but not least: this PR changes the Helm chart slightly, only to make the Helm tests pass in CI. But another PR will introduce a bigger revamp of the Helm chart in order to fully to adapt it to Quarkus.