Include license files in all package distributions

Add NOTICE, DISCLAIMER, and LICENSE files to the stage target
in Makefile to ensure they are included in all package formats
(tar, rpm, and deb). This ensures proper license attribution and
compliance with Apache Software Foundation requirements for all
distribution methods.

Previously, these files were not copied during the packaging
process, which could lead to incomplete license information in
distributed packages.

Author: tuhaihe

Makefile

@@ -115,6 +115,7 @@ endif
 	cp -a server/build/stage/* build/stage/$${PXF_PACKAGE_NAME} ;\
 	echo $$(git rev-parse --verify HEAD) > build/stage/$${PXF_PACKAGE_NAME}/commit.sha ;\
 	cp package/install_binary build/stage/$${PXF_PACKAGE_NAME}/install_component ;\
+	cp NOTICE DISCLAIMER LICENSE build/stage/$${PXF_PACKAGE_NAME}/ ;\
 	echo "===> PXF staging is complete <==="
 
 tar: stage