This commit limits the output in the json pipeline to a "reasonable"
length. We ran into issues (e.g. [0]) from a combination of a stage
that produce tons of output (dracut, ~256 kb, see issue#1976) and
the consumer ("images" osbuild/monitor.go) that used a golang scanner
with a max default buffer of 64kb before erroring. So limit it
here.
The stage result from via json is mostly for information and any error
will most likely at the end. Plus consumers can collect the individual
log lines on their own if desired via the "log()" messages that are
stream in "real-time" with the added benefit that e.g. timestamps
can be added to the logs etc.
[0] https://issues.redhat.com/browse/RHEL-77988
b22cbd3298