Add "Tabs" option to the toolbar

[MashaMSFT]

It'd be cool if adding a "Tab" is an option in the toolbar:

so there'd be a "tab" option that, when you select it, you tell it the h2 level, and then what tabs you wana use, and then it automatically generates something like the following:

## [Portal](#tab/azure-portal)
## [PowerShell](#tab/powershell)
## [Azure CLI](#tab/azure-cli)

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I always have to look up the syntax whenever i add a tab so it'd be cool if the authoring pack did it for me :)

thanks!