[GCU] Turning port admin down before some critical port changes (#1998)

#### What I did
Fixes #1930 

Issue can be summarized into these 2 case:
* A patch can contain an operation to turn port `admin up` -- do at the end
* A patch that modifies config that needs the port to be down -- start by bringing the port down then do the update then bring it back up

#### How I did it
The configs that need the port to be down, we will call them `critical-port` configs.

* Added a move validator to validate `critical-port` configs, which does the following
  * If a port is up, make sure the move does not make changes to related `critical-port` configs
  * If the move is turning a port up, make sure there is no `critical-port` config are still left in the patch

* Added a move extender to `critical-port` changes:
  * If a port is up, bring down if there are critical-port changes
  * If the move is turning a port up, flip it to down if there are still `critical-port` configs left. In other words, do not turn the port back up until all `critical-port` changes are in done.

#### How to verify it
* Added `AddRack` unit-test to `tests/generic_config_updater/files/patch_sorter_test_success.json`
* Other unit-tests

#### Previous command output (if the output of a command-line utility has changed)
Check issue #1930 for old sorting order

#### New command output (if the output of a command-line utility has changed)
Check  `AddRack` unit-test to `tests/generic_config_updater/files/patch_sorter_test_success.json` for new sorting-order

generic_config_updater/gu_common.py

@@ -273,7 +273,13 @@ def create_path(self, tokens):
         return JsonPointer.from_parts(tokens).path
 
     def has_path(self, doc, path):
-        return JsonPointer(path).get(doc, default=None) is not None
+        return self.get_from_path(doc, path) is not None
+
+    def get_from_path(self, doc, path):
+        return JsonPointer(path).get(doc, default=None)
+
+    def is_config_different(self, path, current, target):
+        return self.get_from_path(current, path) != self.get_from_path(target, path)
 
     def get_xpath_tokens(self, xpath):
         """
@@ -548,7 +554,8 @@ def _get_xpath_tokens_from_leaf(self, model, token_index, path_tokens, config):
             # Source: Check examples in https://netopeer.liberouter.org/doc/libyang/master/html/howto_x_path.html
             return [f"{token}[.='{value}']"]
 
-        raise ValueError("Token not found")
+        raise ValueError(f"Path token not found.\n  model: {model}\n  token_index: {token_index}\n  " + \
+                         f"path_tokens: {path_tokens}\n  config: {config}")
 
     def _extractKey(self, tableKey, keys):
         keyList = keys.split()
@@ -712,7 +719,8 @@ def _get_path_tokens_from_leaf(self, model, token_index, xpath_tokens, config):
             list_idx = list_config.index(leaf_list_value)
             return [leaf_list_name, list_idx]
 
-        raise Exception("no leaf")
+        raise ValueError(f"Xpath token not found.\n  model: {model}\n  token_index: {token_index}\n  " + \
+                         f"xpath_tokens: {xpath_tokens}\n  config: {config}")
 
     def _extract_key_dict(self, list_token):
         # Example: VLAN_MEMBER_LIST[name='Vlan1000'][port='Ethernet8']