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`
- Add PMD checks and resolve failing rules
- Apply Spring Checkstyle rules based on Spring Framework
- Rearrange imports to be more consistent
- Format whitespace
