Reliable way to debug core dumps

[cole-miller]

We should have a reliable recipe for running GDB using the executable uploads and core dumps that are produced by Jepsen (and uploaded by GHA) in case of an assertion failure, segfault, etc. I've just been trying to do this with the failure artifact for canonical/raft#470, copying the binary and core dump into a Docker container that uses ghcr.io/canonical/jepsen-dqlite-unofficial and in which I've installed libraft.so and libdqlite.so under /usr/local/lib; GDB still fails to read the shared object list for the app binary (ldd runs fine).