[Go] update dotprompt model strings to use provider/model (#94)

* [Go] update dotprompt model strings to use provider/model

Also update coffee-shop to use GOOGLE_GENAI_API_KEY rather than GEMINI_API_KEY.

go/ai/generator.go

@@ -74,8 +74,8 @@ type generatorActionType = genkit.Action[*GenerateRequest, *GenerateResponse, *C
 
 // LookupGeneratorAction looks up an action registered by [RegisterGenerator]
 // and returns a generator that invokes the action.
-func LookupGeneratorAction(name string) (Generator, error) {
-	action := genkit.LookupAction(genkit.ActionTypeModel, name, name)
+func LookupGeneratorAction(provider, name string) (Generator, error) {
+	action := genkit.LookupAction(genkit.ActionTypeModel, provider, name)
 	if action == nil {
 		return nil, fmt.Errorf("LookupGeneratorAction: no generator action named %q", name)
 	}

go/genkit/dotprompt/genkit.go

@@ -184,8 +184,12 @@ func (p *Prompt) Execute(ctx context.Context, input *ActionInput) (*ai.GenerateR
 		if model == "" {
 			return nil, errors.New("dotprompt action: model not specified")
 		}
+		provider, name, found := strings.Cut(model, "/")
+		if !found {
+			return nil, errors.New("dotprompt model not in provider/name format")
+		}
 
-		generator, err = ai.LookupGeneratorAction(model)
+		generator, err = ai.LookupGeneratorAction(provider, name)
 		if err != nil {
 			return nil, err
 		}

go/samples/coffee-shop/main.go

@@ -72,9 +72,9 @@ type testAllCoffeeFlowsOutput struct {
 }
 
 func main() {
-	apiKey := os.Getenv("GEMINI_API_KEY")
+	apiKey := os.Getenv("GOOGLE_GENAI_API_KEY")
 	if apiKey == "" {
-		fmt.Fprintln(os.Stderr, "coffee-shop example requires setting GEMINI_API_KEY in the environment.")
+		fmt.Fprintln(os.Stderr, "coffee-shop example requires setting GOOGLE_GENAI_API_KEY in the environment.")
 		fmt.Fprintln(os.Stderr, "You can get an API key at https://ai.google.dev.")
 		os.Exit(1)
 	}
@@ -86,7 +86,7 @@ func main() {
 	simpleGreetingPrompt, err := dotprompt.Define("simpleGreeting",
 		&dotprompt.Frontmatter{
 			Name:  "simpleGreeting",
-			Model: "google-genai",
+			Model: "google-genai/gemini-1.0-pro",
 			Input: dotprompt.FrontmatterInput{
 				Schema: jsonschema.Reflect(simpleGreetingInput{}),
 			},
@@ -121,7 +121,7 @@ func main() {
 	greetingWithHistoryPrompt, err := dotprompt.Define("greetingWithHistory",
 		&dotprompt.Frontmatter{
 			Name:  "greetingWithHistory",
-			Model: "google-genai",
+			Model: "google-genai/gemini-1.0-pro",
 			Input: dotprompt.FrontmatterInput{
 				Schema: jsonschema.Reflect(customerTimeAndHistoryInput{}),
 			},