Create modern site.

• command: spo site add --type [type] -u|--url [url] -a|--alias [alias] -t|--title <title> -d|--description [description] -c|--classification [classification] --allowFileSharingForGuests --siteDesign [siteDesign] --siteDesignId [siteDesignId] --isPublic
• type - type of site to create. Allowed values TeamSite|CommunicationSite. Default TeamSite. The selected site type determines the required and applicable options.

Options for TeamSite:

• title - site title, required
• alias - site alias, required, used for the URL and name of the associated group
• description - site description, optional
• classification - site classification, optional
• isPublic - determines if the associated group is public or not

Options for CommunicationSite:

• title - site title, required
• url - site url, required
• description - site description, optional
• classification - site classification, optional
• allowFileSharingForGuestUsers - determines whether it's allowed to share file with guests, optional
• siteDesign - type of communication site to create, optional. Allowed values Topic|Showcase|Blank. Each value resolves to a GUID: Topic=Guid.Empty, Showcase=6142d2a0-63a5-4ba0-aede-d9fefca2c767, Blank=f6cc5403-0d63-442e-96c0-285923709ffc
• siteDesignId - id of the custom site design to use to create the site
  Either siteDesign or siteDesignId is required

For more information see:

https://github.com/SharePoint/PnP-Sites-Core/blob/62d3a007ea4f52d4715ce57928928ebe0e0b06b7/Core/OfficeDevPnP.Core/Sites/SiteCollection.cs#L28
https://github.com/SharePoint/PnP-Sites-Core/blob/62d3a007ea4f52d4715ce57928928ebe0e0b06b7/Core/OfficeDevPnP.Core/Sites/SiteCollection.cs#L126