Add optional AccessMode to StorageResourceMappingItem

[mansam]

konveyor/virt-controller would like to be able to specify a supported access mode when creating storage/disk mappings. This adds an AccessMode field to the StorageResourceMappingItem, and adds support for mapping the AccessMode and VolumeMode in the vSphere provider.

AccessMode and VolumeMode will default respectively to ReadWriteOnce and Filesystem in the vSphere provider.
The oVirt provider will take the access mode from the mapping if it's set, otherwise it will determine the access mode as it previously did.

[kubevirt-bot]

@mansam: Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

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[kubevirt-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: mansam, pkliczewski
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