kernel.CreateSemanticFunction functionName is marked optional, but is not optional

[bkrabach]

Describe the bug If using the overload for kernel.CreateSemanticFunction that takes a PromptTemplateConfig, the functionName is marked optional, but if you execute the code it will throw an exception that functionName is not optional.

If you use the overload that takes just a promptTemplate (everything else optional), then you omit the functionName and when executing it will work, despite not having a functionName defined.

@shawncal

[dluc]

#849 should fix this too

[craigomatic]

Closing given #849 - please reopen if needed!