Adjust CSRv3 CDDL after implementation experience

Rename from AuthenticatedMessage to AuthenticatedRequest in order to
make the direction of the message clear.

Move the challenge out of the endpoint-specific message and up into the
common authentication wrapper as it is uesd in the authentication
protocol.

Simplify the versioning by having the CSR version continue sequentially,
making the current version 3. Have the AuthenticatedMessage version
start from 1 as it's value isn't used to distinguish v2 and v3 CSRs
anyway and it will avoid confusion with the CSR version which has
already moved beyond this value.

Bug: 250910137
Test: n/a -- comments only
Change-Id: I13836e90fa76b1b22cb6627f3d987828ffeb0adc