Merge shared library into casc repo

There's currently multiple shared libraries, with only one being used [1]. However, it's not really used as a shared library, only a different repo where some jenkins functionality is stored. We should merge that repo with the main jenkins-csb-declaration code-base to ease pipeline development.

 [1] https://gitlab.cee.redhat.com/istio/servicemesh-qe/jenkins-shared-library