Change handlebar template to correct format for nested function calling

[sandeepvootoori]

Updating the docs and sample to reflect the change for correct nested function calling template in handlebars

[learn-build-service-prod[bot]]

Learn Build status updates of commit 2cf42bf:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
samples/dotnet/05-Nested-Functions-In-Prompts/Program.cs	:white_check_mark:Succeeded
semantic-kernel/prompts/calling-nested-functions.md	:white_check_mark:Succeeded

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[dengyakui]

@sandeepvootoori : the following line 67-70 has the same issues for history parameter and I found another problems ,the history parameter value in SummaryPlugin.SummarizeConversation is always the object type string, not the history items, so the plugin can not summarize by the type string code.

https://github.com/sandeepvootoori/semantic-kernel-docs/blob/2cf42bf6c491b749f53132eeaa0a538d688e85ff/samples/dotnet/05-Nested-Functions-In-Prompts/Program.cs#L66

// Create a Semantic Kernel template for chat
var chat = kernel.CreateFunctionFromPrompt(
    @"{{ConversationSummaryPlugin.SummarizeConversation $history}}
    User: {{$request}}
    Assistant: "
);