ctf: Add a benchmark trace enum

And add a first trace to be used for benchmarks. These traces are too
big to be added to the test traces repo, so they should be optional
resources to download to run some benchmarks on.

Change-Id: Icba00c9a49fb81d9ed86485dc7e2d9890655c0e4
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/91917
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>