Chinmay,
the Azure Powershell module documentation can be found here.
Unfortunately, it doesn't look like the ability to create a web app bot is included.
If you've ever created a bot manually in the Azure portal, then you know that a bot actually consists of several azure resource types like an app service, a bot service, etc.
I would like to see the ability in powershell myself.
If you're interested, the Azure CLI tools DO support bot creation and managements. az bot commands are available in that toolset. Documentation can be found here.
