Tweaks to anonymous user ID code path monitoring (#26194)
Tweaks to anonymous user ID code path monitoring (#26194)

- Use different attribute names for new and old versions of function
- Use a shorter name overall (for ease of analysis)
- Add monitor for fetched-existing case
- Only record computed-stored if `get_or_create` succeeds, but also
  break it into created vs. fetched cases by checking return value
- Correct name of monitor in `except` clause -- that should only happen
  for a race inside `get_or_create` itself. There's a different race in
  the `anonymous_uid_for_user` between fetch and compute/save.
- Other name tweaks

ARCHBOM-1674
arbrandes/edx-platform,stvstnfrd/edx-platform,eduNEXT/edx-platform,angelapper/edx-platform,arbrandes/edx-platform,EDUlib/edx-platform,edx/edx-platform,eduNEXT/edunext-platform,angelapper/edx-platform,eduNEXT/edunext-platform,EDUlib/edx-platform,angelapper/edx-platform,edx/edx-platform,eduNEXT/edx-platform,arbrandes/edx-platform,edx/edx-platform,eduNEXT/edx-platform,EDUlib/edx-platform,stvstnfrd/edx-platform,stvstnfrd/edx-platform,eduNEXT/edx-platform,stvstnfrd/edx-platform,arbrandes/edx-platform,eduNEXT/edunext-platform,eduNEXT/edunext-platform,angelapper/edx-platform,EDUlib/edx-platform,edx/edx-platform