Add defensive checks against URI parameters in the public API

[sentry]

Observed behavior

Requests to the public APIs, such as /api/public/v2/contentnode_tree/8f0a5b9d89795/, that have an invalid UUID cause a 500 error.

Sentry Issue: STUDIO-HH7

ValueError: badly formed hexadecimal UUID string
(23 additional frame(s) were not displayed)
...
  File "kolibri_public/views.py", line 65, in wrapper_func
    response = some_func(*args, **kwargs)
  File "kolibri_public/views.py", line 700, in retrieve
    queryset = self.get_tree_queryset(request, pk)
  File "kolibri_public/views.py", line 646, in get_tree_queryset
    if pk and self.filter_queryset(self.get_queryset()).filter(id=pk).exists()
  File "kolibri_content/fields.py", line 159, in get_db_prep_value
    value = uuid.UUID(value)

Expected behavior

This error is caused by 'bad input', which we still don't want to accept. Although, since the error causes a 500 response, it would be better for us to validate any request input matches what we expect, which in this case the request parameter looks like a UUID, and return a 'Bad Request' response instead. We should do this for all the public APIs.

[rtibbles]

See here for how this was handled in Kolibri, many of the same strategies should be workable here: learningequality/kolibri#11009

[rtibbles]

Fixed in #4794