Update samples to advise users to use CreateDefaultBuilder

### Description

We should update samples to advise users to use `Host.CreateDefaultBuilder()`

This will include user secrets, validate scopes, as well as other defaults.

This will address these two issues as it will bring in the expected items by default:

- https://github.com/Azure/azure-functions-dotnet-worker/issues/2661
- https://github.com/Azure/azure-functions-dotnet-worker/issues/606

Start by locating the sample projects that configure the host and compare their current setup with the issue's requested Host.CreateDefaultBuilder() usage. Review issues 2661 and 606 for the expected defaults, then verify that the samples consistently advise the requested builder and cover those concerns.

Written by the indexing model from the issue text.