fix: split attestation bits from metsys plugin

[miki725]

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• PR title uses semantic commit messages
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• Updated CHANGELOG.md if necessary

Issue

push report for non-chalked image had some keys missing such as _CHALK_RUN_TIME

Description

currently metsys plugin was reporting global metadata keys such as chalk run time as well as generating attestation bits such as artifact signature.

this meant that disabling metsys plugin to avoid assigning metadata id, etc would also not report global keys such as chalk run time

this was happening for docker push when pushing non-chalked image

Testing

➜ make tests args="test_docker.py::test_push_nonchalked --logs"