Investigate/replace thread local usage in _RequestCache

[ormsbee]

This is not async-friendly:

edx-django-utils/edx_django_utils/cache/utils.py

Lines 43 to 51 in fe75e97

	class _RequestCache(threading.local):
	"""
	A thread-local for storing the per-request caches.
	The data is a dict of dicts, keyed by namespace.
	"""
	def __init__(self):
	super().__init__()
	self._data = {}