[CI] Include build log's url in the nightly crossbow report

[asfimport]

The github statuses/checks API contains additional context about the builds, including the build log's URL (though this may depend on the actual CI service).

We should extend the nightly report to include the build log's URL only for the failing tasks.

Reporter: Krisztian Szucs / @kszucs

_{Note: This issue was originally created as ARROW-12819. Please see the migration documentation for further details.}

[asfimport]

Jacob Wujciak / @assignUser:
CC @raulcd