ci: add abipkgdiff check
ci: add abipkgdiff check

abipkgdiff is a tool capable of comparing two library packages and tell
if one of them introduced ABI-breaking changes.

Plain abidiff is also available, but since we already build Debian
packages I thought it would be more convenient to use pkg version.

This currently works only for pull requests.

oktal/rest,oktal/rest,oktal/rest,oktal/rest