Add CLI examples for Amazon Managed Grafana workspace operations

[sushilk123]

Description

Adds missing CLI examples for Amazon Managed Grafana service commands to improve documentation coverage.

Changes

• Add create-workspace example showing basic and advanced workspace creation with data sources
• Add describe-workspace example for retrieving detailed workspace information and configuration
• Add update-workspace example for modifying workspace settings and data source configurations
• Improves documentation coverage for Amazon Managed Grafana service from 1 to 4 examples

Testing

Examples follow existing AWS CLI documentation format and provide realistic use cases for essential Grafana workspace management including creation, inspection, and configuration updates.