Create if-none-match tag

[vilit1]

Replace logic for replace tag with if-none-match

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[digimaun]

We can make this a bit more clear: "Indicates the create operation should fail if an existing twin with the same id exists."

[digimaun]

Let's add at least one command example & description for each command that can make use of --if-none-match or --etag

https://github.com/vilit1/azure-iot-cli-extension/blob/if_none_match/azext_iot/digitaltwins/_help.py

[digimaun]

Let's add an integration test to exercise --if-none-match for az dt twin relationship create

[vilit1]