[Az CLI] Add support for Node 12

[ahmedelnably]

Scenarios we care about:

Creation of Node 12 app
Validation that versions match on publishing
When a user upgrades to V3, ensure that their Node versions are compatible

[ahmedelnably]

Azure/azure-cli#11364

[fabiocav]

@dariagrigoriu @ahmedelnably this will be completed next sprint.

[fabiocav]

This is currently in PR here: Azure/azure-cli#11987

[gzuber]

PR has been merged