component/onlyoffice_core: update download URL
The previous URL pattern is 404 with current gitlab, this is working today probably because it is in shacache.
Updating the download URL to the new URL pattern produces a tarball with a different checksum. Unlike github and unlike my assumptions, gitlab does not guarantee hash stability for archives ( https://gitlab.com/gitlab-org/gitlab/-/issues/402616#note_1330840501 )
To keep the exact same file, I downloaded it from shacache and uploaded it in a gitlab registry release, following https://lab.nexedi.com/help/user/packages/generic_packages/index.md
At the same time, the repository was moved from bk namespace to nexedi namespace