Migrate CI coverage for test builds from openclover to a Java11+ compatible coverage tool

OpenClover (https://github.com/openclover/clover) does not currently have support for Java 11+ source & bytecode compatibility, which means we can no longer use it for Jalview 2.12 onwards.

We need to:

1. look around for a suitable alternative (JaCoCo looks like it is being used by other projects for coverage, however its reports do not directly integrate with Bamboo. )
2. Decide if its worth migrating to the alternative, or instead dropping coverage from the CI build alltogether.