nightly-metrics

test: set up itk nightly runs (#1052)

# Description

This PR:

* configures nightly runs for itk tests
* uploads the results to `nightly-metrics` rolling release to be re-used
for visual inspection
* separates test cases definition from execution script

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Fixes #<issue_number_goes_here> 🦕

Co-authored-by: Krzysztof Dziedzic <dziedzick@google.com>