Tests: flt.lttng-utils.debug-info: update debug-info tests

* Convert the currently disabled Python bindings based debug-info
  testcase to a `sink.text.details` based test.
* Update debug-info test trace using a recently changed `libhello_so`
  file.
* Move all debug-info test files to
  `tests/plugins/flt.lttng-utils.debug-info/`
* Move `tests/data/debug-info/README.md` content to `CONTRIBUTING.adoc`
* Update `tests/data/plugins/flt.lttng-utils.debug-info/README.md` to
  explain how to generate the debug-info test trace.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I67b8fa729e462137fb3e584c0f1eaf472256e3c9
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1704
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>