Context:
To align our supported environments with the CamBPM Platform JDK 13 support needs to be added.
AT:
- remove JDK 12 compatibility as it reached EOL
- remove 12 from java compatibility test pipeline
- announce dropped support
- add dropped JDK 12 support to upgrade notes
- add OpenJDK 13 & Adopt OpenJDK 13 support
- java compatibility test pipeline stages are added
- new compatibility is announced on https://docs.camunda.org/enterprise/announcement/#camunda-optimize-announcements
- compatibility is mentioned in the supported environments docs https://docs.camunda.org/optimize/develop/technical-guide/supported-environments/