docs/debugging.md: add 'Throubleshooting' subchapter
docs/debugging.md: add 'Throubleshooting' subchapter

To the 'Debugging Scylla with GDB' chapter.

scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla