[GCU] Ignore bgpraw in GCU applier (sonic-net#2623)

What I did
show run all output will include bgpraw for business needs. GCU ipv6 test will update BGP_NEIGHBOR table which caused bgpraw content change, which will make the apply-patch operation fail. The solution is to add bgpraw to ignored tables.

How I did it
Add new added bgpraw table to ignored backend table.

How to verify it
Existing Unit test and local E2E GCU test.

Author: wen587

generic_config_updater/change_applier.py

@@ -76,6 +76,7 @@ class ChangeApplier:
     def __init__(self):
         self.config_db = get_config_db()
         self.backend_tables = [
+            "bgpraw",
             "BUFFER_PG",
             "BUFFER_PROFILE",
             "FLEX_COUNTER_TABLE"