Expose channel names from ChannelAxis (#26)

* Copy list

* Update ChannelAxis.java

Author: alanocallaghan

src/main/java/qupath/bioimageio/spec/tensor/axes/ChannelAxis.java

@@ -16,6 +16,7 @@
 
 package qupath.bioimageio.spec.tensor.axes;
 
+import java.util.ArrayList;
 import qupath.bioimageio.spec.tensor.sizes.FixedSize;
 import qupath.bioimageio.spec.tensor.sizes.Size;
 import qupath.bioimageio.spec.tensor.BaseTensor;
@@ -43,6 +44,14 @@ public void validate(List<? extends BaseTensor> tensors) {
         // fixed size based on list of channels
     }
 
+    /**
+     * Get the list of channel names
+     * @return a copy of the underlying list of channel names
+     */
+    public List<String> getChannelNames() {
+        return new ArrayList<>(channel_names);
+    }
+
     @Override
     public AxisType getType() {
         return AxisType.C;