New command: update site classification #304

Update site classification

• command: graph siteclassification set -c|--classifications [classifications] -d|--defaultClassification [defaultClassification] --usageGuidelinesUrl [usageGuidelinesUrl]
• classifications: comma-separated list of classifications to enable in the tenant
• defaultClassifications: classification to use by default
• usageGuidelinesUrl: URL with additional information that should be displayed when choosing the classification for the given site
• requires connection to the Microsoft Graph (Add support for authenticating to MS Graph #10)

For more information see the Update-PnPSiteClassification cmdlet