Get-DiskByIdentifier: Allow selection based on Serial Number

[bozho]

Pull Request (PR) description

This PR introduces support for using disk serial number as a disk identifier in disk-related resources Disk, DiskAccessPath and WaitForDisk.

This Pull Request (PR) fixes the following issues

• Fixes #259

Task list

• [x] Added an entry under the Unreleased section of the change log in the CHANGELOG.md. Entry should say what was changed, and how that affects users (if applicable).
• [x] Resource documentation added/updated in README.md in the resource folder.
• [x] Resource parameter descriptions added/updated in schema.mof and comment-based help.
• [x] Comment-based help added/updated.
• [ ] Localization strings added/updated in all localization files as appropriate.
• [ ] Examples appropriately added/updated.
• [ ] Unit tests added/updated. See DSC Resource Testing Guidelines.
• [ ] Integration tests added/updated (where possible). See DSC Resource Testing Guidelines.
• [x] New/changed code adheres to DSC Resource Style Guidelines and Best Practices.

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This change is 

[bozho]

Need to add more tests

[PlagueHO]

This has been superseded by #271 .