Use two queues for PRACH processing:

- prach_ru_queue: pass jobs from TX thread (scheduler) to RU thread. For
  split 8, the RU thread itself handles PRACH processing; for split 7.2,
  it is the library that is responsible for handling PRACH messages (see
  oran_fh_if4p5_south_in())
- prach_l1rx_queue: after jobs have been handled in RU thread, use this
  queue to pass jobs to the RX thread. There, preamble detection is
  performed, and RACH.indication FAPI messages are filled if a preamble
  has been detected.

Together, these queues replace a linear search in a global array that
has been modified by three threads at the same time. The design ensures
that access now is thread-safe, and with less overhead.
Signed-off-by: Robert Schmidt <robert.schmidt@openairinterface.org>