azurerm_powerbi_embedded - improve the error message for name validation

internal/services/powerbi/validate/embedded_name.go

@@ -12,7 +12,7 @@ func EmbeddedName(v interface{}, k string) (warnings []string, errors []error) {
 	value := v.(string)
 
 	if !regexp.MustCompile(`^[a-z][a-z0-9]{3,63}$`).MatchString(value) {
-		errors = append(errors, fmt.Errorf("%q must be between 4 and 64 characters in length and contains only lowercase letters or numbers.", k))
+		errors = append(errors, fmt.Errorf("%q must be between 4 and 64 characters in length and starts with a letter and contains only lowercase letters or numbers.", k))
 	}
 
 	return warnings, errors