Print message when retry loop recovers; enable upgrade messages

- Make it clear when the retry loop successfully recovered a request.

- Initialize logging to include info messages (previously logging was
  initialized in app_builder as an import side effect, to include
  warning messages only). This has the side effect of re-enabling
  messages about server-side recommended upgrades.
PTFM-8759 Eliminate import-time side effects from dxpy.current_job

* Remove top level attributes `dxpy.current_job`, `dxpy.current_app`,
  `dxpy.current_applet`
* Introduce accessor methods
  `dxpy.utils.exec_utils.get_current_job()`,
  `dxpy.utils.exec_utils.get_current_executable()`
* Add tests
* Add an autodoc section for `dxpy.utils` and submodules
* Update autodoc build dependencies