Remove extension helpers, instead use parameters for passwords.

[IEvangelist]

Remove extension helpers, instead use parameters:

• Related to https://github.com/dotnet/docs-aspire/issues/672

[davidfowl]

We should be doing 2 things:

1. Removing the explicit parameters
2. Explaining to people how to set the built in parameters using user secrets.

[IEvangelist]

Discussed this offline with @davidfowl - closing this in favor of an alternative approach to update the docs, with local-code snippets that tell the story a bit more precisely.