Extend the 'spo page add' command with support for promoting as template. `spo page add --promoteAs Template` Equivalent of the `PromoteAs Template` option in the [Add-PnPClientSidePage](https://github.com/SharePoint/PnP-PowerShell/blob/fc5b2ac57721262a10b56dc4ead49fde14955b92/Commands/ClientSidePages/AddClientSidePage.cs) cmdlet.
Extend the 'spo page add' command with support for promoting as template.
spo page add --promoteAs TemplateEquivalent of the
PromoteAs Templateoption in the Add-PnPClientSidePage cmdlet.