Previously we ran manual jobs automatically in the `cmake/cmake`
project integration branches. Change this to happen only when
the pipeline is created by a schedule.
Also, start automatic jobs in scheduled pipelines without delay.
When running a pipeline on an integration branch in `cmake/cmake`, delay
the lint jobs just as much as all the others. This avoids starting them
unnecessarily during a sequence of merges over a short time range.
GitLab 13.3 started creating MR pipelines in the parent project of a MR
from a fork, at least when the MR submitter is a developer in the parent
project. If the pipeline is associated with a MR, we should use the
corresponding rules regardless of which project hosts the pipeline.
Also add comments for sections to make it easier to figure out what's
going on.
Also rename the `cmake_test_unix_package` to be Linux-specific since it
actually is.