Add command to get an attachment (#1080)

* Add command to get an attachment

* Refactor retrieving of attachments to use StreamDetails

* Refactor AttachmentCommand to GetAttachmentCommand

* Minor improvements to GetAttachmentCommand

* Use JSON serializer to serialize binary data

Serializing the stream is better for memory handling than
loading the whole thing into the file.

* Clean up unneeded class

* Added command to doc

Co-authored-by: cedb <cedb@keylimebox.org>

src/main/java/org/asamk/signal/dbus/DbusManagerImpl.java

@@ -46,6 +46,7 @@ import org.freedesktop.dbus.types.Variant;
 
 import java.io.File;
 import java.io.IOException;
+import java.io.InputStream;
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.time.Duration;
@@ -916,6 +917,11 @@ public class DbusManagerImpl implements Manager {
         }).toList();
     }
 
+    @Override
+    public InputStream retrieveAttachment(final String id) throws IOException {
+        throw new UnsupportedOperationException();
+    }
+
     @SuppressWarnings("unchecked")
     private <T> T getValue(
             final Map<String, Variant<?>> stringVariantMap, final String field