Add Delay Mechanism for Initial MIB/SIB Transmission in gNB Scheduler

This commit introduces a delay mechanism for the first MIB/SIB transmission
in the gNB scheduler to allow PRACH noise estimate to converge stabilize
before first PRACH preamble reception.

Key changes:
- Added the `num_scheduled_prach_rx` variable to gNB_MAC_INST to keep track
  of total number scheduled of PRACH receptions. Using uint64_t type to avoid
  overflow.
- Updated the `gNB_dlsch_ulsch_scheduler` function to conditionally schedule
  MIB/SIB transmissions if `num_scheduled_prach_rx` is at least 100.
  The value comes from OAIs implementation of PRACH noise estimate.

common/platform_constants.h

@@ -93,5 +93,6 @@
 #define RETURNerror (-1)
 #define DEFAULT_NAS_PATH "PWD"
 #define UNUSED_VARIABLE(vARIABLE) (void)(vARIABLE)
+#define NUM_PRACH_RX_FOR_NOISE_ESTIMATE 100
 
 #endif /* __PLATFORM_CONSTANTS_H__ */