[PowerShell 7.4 Breaking Change] Document case-sensitivity breaking change

In `PowerShell 7.0` and `7.2`, `ConvertFromJson` returns a case-sensitive hashtable by design. In Azure Functions `PowerShell 7.0` and `7.2`, we take the output of `ConvertFromJson` and try to cast it to a case-insensitive hashtable to support deserializing JSON which may contain keys that only differ in case.

Starting `PowerShell 7.3` or higher, the output of `ConvertFromJson` returns an ordered hashtable. The constructor of `OrderedHashtable` does not support creating a case-insensitive ordered hashtables. As a result, in Azure Functions `PowerShell 7.4`, we will no longer wrap the output of `ConvertFromJson`, so the return type will be an `OrderedHashtable`. **This is a breaking change.**

For users that need to be able to deserialize JSON with keys that only differ in case, we will provide a cmdlet as part of the Azure.Functions.PowerShell.SDK.