Use rpcBaseUrl in durable operations when possible

[andystaples]

Issue describing the changes in this PR

When experimenting with https://github.com/Azure/azure-functions-durable-powershell/issues/73, I found that if a user does not explicitly call Import-Module on the external SDK, functions that are exposed in the external Durable SDK are not used, and instead the definitions loaded in the bundled module are used.

This change imports the fix from https://github.com/Azure/azure-functions-durable-powershell/pull/66 into the bundled module, with additional checks to prevent breaking backwards compatibility.

Pull request checklist

• [x] My changes do not require documentation changes
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• [ ] My changes should not be added to the release notes for the next release
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