send crustgather output to dedicated file

Arnaud Boutsrequested to merge
1715-crust-gather-ci-issues into main

What does this MR do and why?

Crustgather is to verbose to write output in stdout/stderr. It broke CI display.

The output is written in crustgather.log file stored in the artifact per cluster.

Related reference(s)

Closes #1715 (closed)

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