Extend Repository service to allow more operations and pluggable storage

Currently the service for work items repository is sort of read only mode https://github.com/kiegroup/jbpm-work-items/blob/master/repository/src/main/java/org/jbpm/process/workitem/repository/service/RepoService.java

it needs to be extended to allow pluggable storage mechanism so it can actually "remember" what services were allowed to be used.

In addition it should also provide option to install given service task which would mean

• mark it in the storage as installed
• install work item handler jar file into BC maven repository

Service should also offer some kind of hooks for auto updates of the installed service tasks - mainly in terms of upgrading of the BC to newer version which will then include newer versions of work item handler jars, these needs to be auto installed to maven repo