This is part of a general restructuring in layout of Jenkins job folders
before we can properly introduce Release signing and notarization.
We need this to distinguish between pr/dev builds and release ones to
avoid signing the dev builds with a release certificate.
The meta job managed with `ci/Jenkinsfile.combined` runs a job for all 3
platforms and currently is quite basic, but in the future can be
extended to include - like the mobile one - updating the nightlies page,
or publishing draft GitHub releases.
The addition of `make check-pkg-target-*` steps to other `Jenkinsfile`s
is necessary because the sub-jobs under `platforms` have no option for
checking out Git submodules at the beginning, so I'm making use of how
the `Makefile` works and triggering that with a target that doesn't do much.
Example job:
https://ci.status.im/job/status-desktop/job/release/job/ci-meta-release-job/
Signed-off-by: Jakub Sokołowski <jakub@status.im>
