our CI workflow for publishing the packages expects the tar balls
to be located under `build/$buildMode/dist/tar`, where `$buildMode`
is "release" or "debug".
before this change, the CMake building system puts the tar balls
under "build/dist" when the multi-config generator is used. and
`configure.py` uses multi-config generator.
in this change, we put the tar balls for redistribution under
`build/$<CONFIG>/dist/tar`, where `$<CONFIG>` is "RelWithDebInfo"
or "Debug", this works better with the CI workflow -- we just need
to map "release" and "debug" to "RelWithDebInfo" and "Debug" respectively.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>