Provide sample prompt templates for users

[joshfree]

Some users have to prompt copilot to specify the target tenant as well along with the subscription to ensure Entra ID token is fetched for the tenant where subscription is hosted in.

The target tenant and subscription could be prompted to the LLM once and not have to be repeated for each prompt from the user. this is something that we could provide a prompt template for.

[joshfree]

We should incorporate best practices on .prompt.md files from VS Code docs here https://code.visualstudio.com/docs/copilot/copilot-customization#_prompt-file-structure