Add Java 17 to the CI build and test matrix (towards #401)

[vasiliy-mikhailov]

Towards #401.

What this does

Adds Java 17 to the CI matrix — both the build job (java: [ 11, 17 ]) and all five integration-test categories (new java axis, de-hardcoded setup-java) — so the project builds and is fully tested on 17 alongside 11.

What this deliberately does NOT do

It does not raise source/targetCompatibility (still 11). Following the concern raised in the issue discussion (building with 17 while raising the artifact floor would narrow the user base — as discussed in #401), the bytecode floor stays where it is; raising it remains a 1.0.0 decision for the maintainers. If/when you take it, this matrix is already in place to test it.

Mapping to the issue checklist:

• "If necessary upgrade gradle wrapper" — not necessary: the wrapper is already Gradle 8.5, which runs fine on 17.
• "Update build.gradle / sample-apps poms (source/target)" — intentionally left at 11 per the floor discussion above.
• "Update CI Workflow to build and run using Java 17" — this PR.
• "Update documentation" — found no JDK-requirement statements in the repo docs that need changing; happy to add one if you'd like a supported-JDKs note somewhere specific.

Verification

Locally (Temurin 11 and 17, Docker available for Testcontainers): gradlew build -x integrationTest for core and all six framework modules — green on both JDKs, all unit tests passing (including the Testcontainers-backed configuration tests). The sample-app integration-test categories are exactly what the new CI axis runs.