ARCH-233: Add JWT Auth Middleware.

[robrap]

From edx-drf-extensions:

1. EnsureJWTAuthSettingsMiddleware: Ensures proper JWT auth settings
   for endpoints.
2. JwtAuthCookieMiddleware: Combines the JWT auth cookie parts into a
   JWT auth cookie.

ARCH-233

Credentials Pull Request

Make sure that the following steps are done before rebasing/merging

• Request a review if desired
• Squash/Fixup your branch to one commit
• Config/Dependency Changes (e.g. config files, scripts that are used for provisioning etc.)
  • Make sure you have updated edx/configuration and edx/devstack if necessary
  • Make sure the change builds successfully in a sandbox
• UI Changes
  • Consider other browsers (e.g. Firefox)
  • Check mobile view
  • Consider accessibility (e.g. Run aXe on the page)