Update Snippets to use the latest version

It would be great if we could create some sort of function call that adds in the latest date of a specific resource. The user should of course have the flexibility to change it to whatever they want afterwards.

Example:
VS Code gives us
```
resource virtualNetwork 'Microsoft.Network/virtualNetworks@2019-11-01'
```

but the latest version should be

```
resource virtualNetwork 'Microsoft.Network/virtualNetworks@2021-03-01'
```
It would be awesome of we have make this automatic for our resources to have something like resource virtualNetwork 'Microsoft.Network/virtualNetworks@`LatestVersionOfThisResource()' <-- func

I'm assuming that our latest has the most up to date best practices

The issue names no files, tests, or entry points. First locate how snippets and Azure resource API versions are maintained, then clarify the scope and source of “latest” versions. Done would require an agreed approach that lets users override the selected version and has coverage for the resulting behavior.

Written by the indexing model from the issue text.