fix: analyze command default backend bug (#966)

Now, the default value of the `backend` flag for the analyze command
will be an empty string. And the `NewAnalysis` function has been
modified to use the default backend set by the user if the backend flag
is not provided and the `defaultprovider` is set in the config file.
Otherwise, backend will be set to "openai".

Fixes: https://github.com/k8sgpt-ai/k8sgpt/issues/902

Signed-off-by: VaibhavMalik4187 <vaibhavmalik2018@gmail.com>
Co-authored-by: JuHyung Son <sonju0427@gmail.com>

cmd/analyze/analyze.go

@@ -60,6 +60,7 @@ var AnalyzeCmd = &cobra.Command{
 			withDoc,
 			interactiveMode,
 		)
+
 		if err != nil {
 			color.Red("Error: %v", err)
 			os.Exit(1)
@@ -124,7 +125,7 @@ func init() {
 	// explain flag
 	AnalyzeCmd.Flags().BoolVarP(&explain, "explain", "e", false, "Explain the problem to me")
 	// add flag for backend
-	AnalyzeCmd.Flags().StringVarP(&backend, "backend", "b", "openai", "Backend AI provider")
+	AnalyzeCmd.Flags().StringVarP(&backend, "backend", "b", "", "Backend AI provider")
 	// output as json
 	AnalyzeCmd.Flags().StringVarP(&output, "output", "o", "text", "Output format (text, json)")
 	// add language options for output