time/kunit: Add .kunitconfig

time/kunit: Add .kunitconfig

Add .kunitconfig file to the time directory to enable easy execution of
KUnit tests.

With the .kunitconfig, developers can run the tests:
  $ ./tools/testing/kunit/kunit.py run --kunitconfig kernel/time

Also, add the new .kunitconfig file to the TIMEKEEPING section in the
MAINTAINERS file.

Signed-off-by: Ryota Sakamoto <sakamo.ryota@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260223-add-time-kunitconfig-v1-1-1801eeb33ece@gmail.com