feat: new "Subsonic Minimal Clients" configuration option (#4850)

* Add `.editorconfig` file

Hints to users how to properly indent Go files (my setup was defaulting
to 2 spaces).

* Add Subsonic API minimal config option

This will allow users to specify clients which can operate with or need
the minimum required fields as per the [SubSonic API
spec](https://subsonic.org/pages/api.jsp).

* Return only required fields for Child Objects

For a minimal client, only return the required fields for Child Objects.

* Return only required fields for Playlist objects

* refactor: simplify client list checks and improve playlist response handling

Signed-off-by: Deluan <deluan@navidrome.org>

* test: add unit tests for client list checks and playlist building logic

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: revert Child.IsVideo and Playlist.Public fields from pointer to boolean, and add omitempty to XML tag

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>
Co-authored-by: Deluan Quintão <deluan@navidrome.org>

server/subsonic/responses/.snapshots/Responses Child without data should match OpenSubsonic .XML

@@ -1,5 +1,5 @@
 <subsonic-response xmlns="http://subsonic.org/restapi" status="ok" version="1.16.1" type="navidrome" serverVersion="v0.55.0" openSubsonic="true">
   <directory id="" name="">
-    <child id="1" isDir="false" isVideo="false"></child>
+    <child id="1" isDir="false"></child>
   </directory>
 </subsonic-response>