appengine device attributes list: show them in a cleaner way

display attributes in a human-friendly representation instead
of defaulting to Go's internal one.
Keep consistency with aliases display (see previous commit).

Signed-off-by: Arnaldo Cesco <arnaldo.cesco@gmail.com>

CHANGELOG.md

@@ -5,6 +5,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [24.5.3] - Unreleased
+### Changed
+- `appengine device attributes list`: display attributes in a human-friendly
+  representation instead Go's internal one. Keep consistency with aliases.
+
 ### Fixed
 - `appengine device alias list`: show aliases as a map instead of a list.
   Fix [#275](https://github.com/astarte-platform/astartectl/issues/275).

cmd/appengine/device_attributes.go

@@ -111,8 +111,12 @@ func attributesListF(command *cobra.Command, args []string) error {
 		os.Exit(1)
 	}
 	attributes, _ := attributesRes.Parse()
+	attributesMap, _ := attributes.(map[string]string)
+
+	for k, v := range attributesMap 	{
+		fmt.Printf("%v: %v\n", k,v)
+	}
 
-	fmt.Printf("%v\n", attributes)
 	return nil
 }