Add API Checker

ABI checker tools generate HTML and TXT API compatibility reports of BIND libraries. Comparison is being done between two bind source trees which hold built BIND.

In the CI one version it the reference version defined by BIND_BASELINE_VERSION variable, the latter one is the HEAD of branch under test.

There are two FIXMEs before https://gitlab.isc.org/isc-projects/images/merge_requests/23 gets integrated.