App Broker 2.0.x

Major dependencies updates:
* Spring Boot 3
* Spring Framework 6
* Spring Cloud Open Service Broker 4.0.0-SNAPSHOT
* Java 17
* Gradle 7.6

Dockerfile:
* Update to Ubuntu Jammy
* Bump to OpenJDK 17
* Remove usage of deprecated `apt-key` tool
* Bump all other tools to latest versions (bosh, bbl, credhub etc.)

ATs:
* Pass required java buildpack env var to use Java 17 on CF
* Update `cf login` invocation to work with cf-cli v8

Small improvements:
* Reliable datetime comparison in `InMemoryServiceInstanceStateRepositoryTest`
* Update `.editorconfig` to match existing style
* Add `.sdkmanrc`

.github/workflows/java-8-baseline.yml

@@ -0,0 +1,16 @@
+name: Java 8 baseline build
+
+on:
+  push:
+    branches: [ 1.6.x, 1.5.x, 1.4.x ]
+  pull_request:
+    branches: [ 1.6.x, 1.5.x, 1.4.x ]
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        java: [ '8', '11', '17' ]
+    uses: ./.github/workflows/gradle-build.yml
+    with:
+      java-version: ${{ matrix.java }}