DevTest Labs does not contain the latest Preview API (2018-10-15-preview) spec

Looking at the content for [DevTest Lab](https://github.com/Azure/azure-rest-api-specs/tree/main/specification/devtestlabs/resource-manager/Microsoft.DevTestLab). It is missing the latest Preview API `2018-10-15-preview` that includes a lot more features than the latest `2018-09-15` version. Example properties:

- Support for system assigned managed identities.
- Use existing storage account for the Lab Artifacts instead of the default.
- Encryption using Customer managed keys using the Disk Encryption set.
- Browser Connect via Azure Bastion.
- Specifying a custom resource group for VM Creation.
- Isolation of lab resources. This changes the Storage accounts and key vaults to 'Selected networks only'
- Disabling auto upgrade of custom script extension.

This causes the following warning when developing Bicep module for DTL:

```bicep
Warning BCP081: Resource type "Microsoft.DevTestLab/labs@2018-10-15-preview" does not have types available.
```

However, the latest API `2018-10-15-preview` is used when managing DTL from the Azure Portal and is referenced in the Resource Provider blade


Also, in Resource Explorer


And when querying the RP via PowerShell:


In addition: Both [Template Documentation](https://learn.microsoft.com/en-us/azure/templates/microsoft.devtestlab/2018-09-15/labs?pivots=deployment-language-bicep) and the [API Documentation](https://learn.microsoft.com/en-us/rest/api/dtl/labs) are missing the latest API `2018-10-15-preview` and parameter usage guidance.

Start in specification/devtestlabs/resource-manager/Microsoft.DevTestLab and compare the existing 2018-09-15 specification with the 2018-10-15-preview API described in the issue. Check the Azure Resource Explorer and Resource Provider references for the listed properties. Done means the preview API is represented and the related Bicep warning and documentation gaps are addressed.

Written by the indexing model from the issue text.