ART-11093 Add option to gem assembly only based on x86 nightly

[Ximinhan]

Add ignore_non_x86_nightlies parameter in gem_assembly to only use one accepted x86 nightly
In gen-assembly when only one nightly input, try to get all arches rhcos pullspec based on rhcos version in x86 release

[openshift-ci]

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[openshift-ci]

@Ximinhan: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/security	1193dde	link	false	/test security

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