Improve Azure Services Post-Generation Experience

[xtinah-w]

Post-Generation Experience

Improve Cosmos DB

• [x] Improve the README file about Azure Cosmos DB and how to use it (includes adding the connection code inside the generated project)
• [ ] Add more comments in the code to let the user know they start from here

Improve App Service

• [x] Explain how to use App Service extension in the README (ctrl + shift + p to deploy)

[sibille]

Readme was improved as part of #1505. Leaving open to review if the code needs additional comments.