This changes the default log link visible in resultsdb from task stdio
output to artifactsdir directory (which contains stdio, debug log and
others). This only applies if the task hasn't set artifact in
resultyaml (that overrides the default).
The reasoning is that taskotron stdio has grown larger and larger and
nowadays it's very hard to find relevant task output inside it anyways.
Tasks really need to create specialized logs at least in case of failure
(and all existing ones do). The new default is much better for
a) people debugging a problem - because they have clear access to all
available files
b) tasks with multiple log files which don't want to set any of them as
default (because it would make accessing the other ones much harder) -
with the new solution they see all artifacts in a directory view