[orchagent] Add FEC frame loss ratio monitoring with predictive analytics (#3953)

Implement observed and predicted FEC frame loss ratio calculations, using
real-time metrics and linear regression on codeword error distribution for
comprehensive network link health monitoring.

Key changes:
1. Add port_flr.lua script with dual FLR calculation methods:
  * Observed FLR from real-time uncorrectable codeword ratios
  * Predicted FLR using log-linear regression on FEC symbol error bins S0-S15
2. Update Makefile.am to include port_flr.lua in distribution
3. Modify portsorch.cpp to load FLR plugin alongside existing port rate monitoring
4. Implement statistical filtering and 2-minute calculation intervals
5. Store results in RATES table as FEC_FLR and FEC_FLR_PREDICTED,
   FEC_FLR_R_SQUARED metrics

The predictive algorithm analyzes FEC codeword error patterns across symbol
error bins, applies regression analysis to model error distribution trends,
and extrapolates potential frame loss using IEEE FEC specifications. This
enables early detection of degrading links before complete failure, supporting
proactive network maintenance.


(cherry picked from commit 1b025d5bb323d28901a578599bdccdc8054d0384)

Signed-off-by: Apoorv Sachan <[email protected]>

Author: apoorv-arista

orchagent/Makefile.am

@@ -28,6 +28,7 @@ dist_swss_DATA = \
 		 pfc_restore.lua \
 		 pfc_restore_cisco-8000.lua \
 		 port_rates.lua \
+		 port_flr.lua \
 		 watermark_queue.lua \
 		 watermark_pg.lua \
 		 watermark_bufferpool.lua \