Linter rule: Prefer specifying subnets under as child resources rather than network properties.subnets

See also https://github.com/Azure/bicep/issues/3886

Example:

GOOD:
https://github.com/Azure/bicep/blob/cb2fb8d223862260cfe8bfdc5899477deca3ff7f/docs/examples/101/vnet-two-subnets/main.bicep#L23

```bicep
resource vnet 'Microsoft.Network/virtualNetworks@2020-06-01' = {
name: vnetName
location: resourceGroup().location
properties: {
addressSpace: {
addressPrefixes: [
addressPrefix
]
}
subnets: [
{
name: 'subnet001'
properties: {
addressPrefix: '10.0.0.0/24'
}
}
{
name: 'subnet002'
properties: {
addressPrefix: '10.0.1.0/24'
}
}
]
}
}
```
BAD:
https://github.com/Azure/azure-quickstart-templates/blob/0fc9fbd4407bbb1f58148bdc7247aa095c16b39a/quickstarts/microsoft.network/vnet-two-subnets/main.bicep#L33
```bicep
resource vnet 'Microsoft.Network/virtualNetworks@2020-06-01' = {
name: vnetName
location: location
properties: {
addressSpace: {
addressPrefixes: [
vnetAddressPrefix
]
}
}

resource subnet1 'subnets' = {
name: subnet1Name
properties: {
addressPrefix: subnet1Prefix
}
}

resource subnet2 'subnets' = {
name: subnet2Name
dependsOn: [
subnet1
]
properties: {
addressPrefix: subnet2Prefix
}
}
}
```

Review the linked issue 3886 and the referenced docs/examples/101/vnet-two-subnets/main.bicep and quickstarts/microsoft.network/vnet-two-subnets/main.bicep examples. Determine where Bicep linter rules are defined and tested; done means the rule prefers subnet child resources over network properties.subnets while recognizing the shown good pattern.

Written by the indexing model from the issue text.