docker-compose: add PKG_NAME to PKG_SOURCE

docker-compose: add PKG_NAME to PKG_SOURCE

Before this change, the tarball was downloaded as vVERSION.tar.gz.
For example, it was v2.26.1.tar.gz and that file was put into the dl folder
within the OpenWrt build system.

After this change, the tarball is properly downloaded as NAME-vVERSION.tar.gz.
In this case, it will look like this: docker-compose-v.2.26.1.tar.gz

The advantages of using this:
- Users, developers will know that what they downloaded (it has name and version)
- The tarball will not be overwritten by another package with the same version.

Signed-off-by: Javier Marcet <javier@marcet.info>
Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
[added commit message]