[FEATURE REQ][Monitor accounts] Allow Custom Resource Group Specification for Monitor Accounts

### API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/main/specification/monitor/Microsoft.Monitor.Accounts.Management/typespec/AzureMonitorWorkspace.tsp

### API Spec version

2025-05-03-preview

### Please describe the feature.

🧩Problem Statement
Currently, the Azure Monitor Accounts API does not allow specifying a custom resource group name during deployment. This limitation causes conflicts with governance models that rely on pattern-based resource group naming or pre-existing resource groups.

Additionally, deployments may fail due to policy enforcement when:
- The resource group is auto created without required tags.
- The resource group does not meet organizational compliance rules.

✅ Proposed Solution
Enable the following enhancements to the Monitor Accounts API:
- Allow specifying a resource group name during account creation.
- Support using pre-existing resource groups if they meet required conditions.
- Allow tagging the resource group explicitly as part of the deployment payload to satisfy policy requirements.

💡 Benefits
- Aligns with enterprise governance and naming conventions.
- Reduces deployment failures due to policy non-compliance.
- Improves flexibility and control for infrastructure automation.

Start by reading specification/monitor/Microsoft.Monitor.Accounts.Management/typespec/AzureMonitorWorkspace.tsp and compare the current account creation model with the API version 2025-05-03-preview. Determine how resource group selection, reuse, and tagging are represented in the specification; done means the API contract clearly supports the requested custom resource group behavior and its policy-related requirements.

Written by the indexing model from the issue text.