Add GitHub workflow for integration tests on multiple Java versions

[ZPascal]

Runs the integration tests against a Cloud Foundry deployed on KinD (kind-deployment) in a Java 8/11/17/21 matrix. Every job gets its own Cloud Foundry.

Functionality

• integration-test.yml deploys Cloud Foundry with the setup-cf action of kind-deployment and runs ./mvnw -Pintegration-test test against it. It runs on a schedule (nightly, latest versions on Java 21), manually (workflow_dispatch, optionally with preview) and from ci-java.yml after the build job (Java 21).
• Validation runs deploy the capi-release that matches SUPPORTED_API_VERSION, resolved by .github/scripts/resolve-capi-version.sh and passed to kind-deployment as a chart version override. Preview runs (schedule, or manual with preview) use the latest versions.
• permissions: contents: read, a concurrency group per ref, and a guard so the nightly run only fires in cloudfoundry/cf-java-client.

PostgreSQL connections

All Cloud Foundry components share one PostgreSQL. Its default of 100 connections runs out during a full run (too many clients already), after which UAA and so every test context fails. The workflow asks kind-deployment for postgres-max-connections: '500', which is set when PostgreSQL is installed. That needs cloudfoundry/kind-deployment#516.

Temporary: until #516 is merged, setup-cf and ref point at a commit of the ZPascal/kind-deployment fork that contains it. Once it is merged, repin both to the upstream commit (marked with a TEMPORARY comment in the workflow).

Dependencies

• Merge Adapt the client and the integration tests to the KinD based CAPI #1383 first. It contains the client and test changes the integration tests need on a current CAPI (resources on bits uploads, the Accept header of the UAA browser flows, the new Stack/Space fields, the TCP port range). Without it this workflow is red.
• feat: Make the max_connections of the shared PostgreSQL configurable kind-deployment#516, see above.

[Lokowandtg]

The failures because of "suspended" where addressed with #1371

[Lokowandtg]

The failures because of "missing :resources" might be a problem in kind? As a workaround I added the following line to https://github.com/cloudfoundry/cf-k8s-releases/blob/4500c9dec5007c5c86c630bb86c3bb596e98259c/capi/helm/files/nginx/nginx_external_endpoints.conf#L47
upload_set_form_field "resources" [];
resulting in running tests.