Adds a tiny `openedx.core.djangoapps.staticfiles` app so that
static asset ignore patterns can be coded into configuration rather
than supplied on the command line or coded into pavelib.
Makes it easier to run static asset collection without Paver.
See ADR for details:
openedx/core/djangoapps/staticfiles/docs/decisions/0001-purpose-of-app.rst
Closes: https://github.com/openedx/edx-platform/issues/31658