Added threshold for core code coverage to 80% and added tests and exclusions

Added storage core coverage Added breaking pipeline variable CORE_COVERAGE_THRESHOLD: "80" to break the pipeline if the coverage is less or equal to 80%.

Last pipeline run coverage is 83% for storage-core: https://osdu.pages.opengroup.org/-/platform/system/storage/-/jobs/2804869/artifacts/storage-core/target/site/jacoco/index.html