Edits to README and separation of shared resources from env

[zachcasper]

This pull request significantly improves and expands the README.md documentation for the Radius Customer Support Agent sample. The changes clarify the purpose and architecture of the sample, provide detailed, step-by-step setup instructions for both Bash and PowerShell users, and restructure the walkthrough for better usability. The documentation now includes richer explanations, diagrams, and explicit instructions for all major setup and deployment steps, making it much more accessible for new users.

Key improvements include:

Documentation Structure and Clarity:

• Rewrote and reorganized the introduction to clarify the application's purpose, the role of Radius, and the architectural overview, including new diagrams and explanations.
• Expanded and clarified prerequisites, providing explicit instructions for both Bash and PowerShell users, and added tips for Windows environments.
• Added detailed explanations about Bicep extensions and Resource Types, including how and when to regenerate extensions.

Step-by-Step Setup Enhancements:

• Added new, explicit steps for authenticating Radius to Azure, creating resource groups and environments, registering credentials, and setting up the CLI workspace, with Bash and PowerShell examples. [1] [2]
• Clarified the process for uploading knowledge base documents, including PowerShell instructions, and explained the role of the AI Search indexer. [1] [2]

Deployment and Cleanup Process:

• Improved and detailed the deployment instructions, including expected outputs and explanations of the resources being created or referenced.
• Added comprehensive cleanup instructions to ensure all resources and credentials are fully removed after use.

These changes make the sample much easier to follow, especially for users new to Radius or cloud-native AI application development.