[FEATURE REQ] Deploy Azure container instances into virtual network

**Is your feature request related to a problem? Please describe.**
We'd like to be able to deploy container groups into an existing virtual network using the fluent API. The feature exists but doesn't appear to be supported in Java yet:
https://docs.microsoft.com/en-us/azure/container-instances/container-instances-vnet#deploy-to-existing-virtual-network

**Describe the solution you'd like**
As part of the ContainerGroup definition, add new builder functions .withVnet().withSubnet().

**Describe alternatives you've considered**
Thought about making a system call out to the Azure CLI tool to avoid this library entirely - not viable for my use case.

**Additional context**
When Microsoft publishes new features into preview, it would be great to know the roadmap for when we can expect to be able to use them in the client libs.

**Information Checklist**
Kindly make sure that you have added all the following information above and checkoff the required fields otherwise we will treat the issuer as an incomplete report
- [X] Description Added
- [X] Expected solution specified

Beginne bei der ContainerGroup-Definition und der fluent API und vergleiche dann die angeforderten withVnet()- und withSubnet()-Builder mit der Dokumentation von Microsoft zu existing-virtual-network für Azure Container Instances. Identifiziere das relevante Modell der Client-Bibliothek und die Validierungstests und betrachte das Feature als vollständig, wenn ein vorhandenes virtuelles Netzwerk und Subnetz in einer ContainerGroup-Definition dargestellt und über die Java API verwendet werden können.

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