Changes

release-tarball-build-dist: upgrade from debian 9

Let it use debian bullseye and rename the directory once, so we don't
need to rename it in the future when switching the debian version
again.

The reason I'm doing this now is that building with debian 9 failed
due to obs.osmocom.org related changes. It would be trivial to fix that,
but I decided to rather upgrade to the latest debian version.

Change-Id: Ib6039724a7200abce5252f95407047296b72cd51

release-tarball-build-dist: move osmo-ci code here

Add a jenkins.sh that does the same as the previous lengthy shell
command in the jenkins-job-builder file, and add
osmocom-release-tarballs.sh. This makes it easier to test the
script, and only patching one repository is needed from now on when
changing to a newer debian version.

Depends: osmo-ci I15f6c08b807f1462f91e95b624cdc1aad0592dd6
Change-Id: I4cf66097f508c029f688ec8af1cab2238d42f84f