Add optional backup partner compatibility testing

[ShellyKa13]

What this PR does / why we need it: Generalize tests marked with label PartnerComp to run with configured script used to backup and restore. Added documentation for backup partner explaining what needs to be done in order to run the tests with their backup solution

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #

Special notes for your reviewer:

Release note:

Backup partner compatibility testing

[kubevirt-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[kubevirt-bot]

@ShellyKa13: 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
pull-kvp-functional-test	fa5c47c5858d209f7e78a3c1b20e574ed3e56b54	link	true	/test pull-kvp-functional-test

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[ShellyKa13]

closing for alternative PR