docs: enhance mobile JWT ADR (#30906)

As part of the implementation of this ADR, we determined that we needed
to make some of the endpoints that return JWTs able to produce
asymmetric JWTs as needed, since asymmetric JWTs are a requirement
in certain cases. This ADR update notes this additional consequence.

openedx/core/djangoapps/oauth_dispatch/docs/decisions/0013-mobile-migration-to-jwt.rst

@@ -57,5 +57,6 @@ For migrating the mobile authentication flow from opaque Bearer access tokens to
 
   * We need to check if the JWT was asymmetrically signed by the LMS. We want to ensure that a symmetrically signed JWT, created (signed) by another IDA, could not be compromised and used by an attacker to exchange for a session cookie, which would allow for full compromise of the user.
   * Implementation will involve adding a method to ``edx-drf-extensions`` like ``get_decoded_jwt_from_auth``, but that will decode only asymmetric JWTs.
+  * Auth token endpoints that return a JWT will now take a request parameter that will enable Mobile to request asymmetric JWTs. This will enable old symmetric JWTs to continue to work until they are fully deprecated/removed, but enable Mobile to request asymmetric JWTs for this new case where they are required.
 
 .. _ADR to add grant type in JWT payload: https://github.com/openedx/edx-platform/blob/master/openedx/core/djangoapps/oauth_dispatch/docs/decisions/0014-add-grant-type-in-jwt-payload.rst