doc: rename api-client tutorial, following the canonical pattern

Author: emanuel-schmid

doc/index.rst

@@ -38,7 +38,7 @@ Tutorials
    tutorial/climada_engine_unsequa_helper
    tutorial/climada_engine_Forecast
    tutorial/climada_util_yearsets
-   turorial/climada_api_client
+   turorial/climada_util_api_client
 
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 Developer guide