[yang] support ACL ACCEPT action (#9784)

Why I did it
ACL have ACCEPT action indeed, but yang doesn't support it.

How I did it
Add 'ACCEPT' enum to sonic-types.yang.j2

How to verify it
Run the YANG model unit tests

src/sonic-yang-models/tests/yang_model_tests/tests/acl.json

@@ -102,5 +102,8 @@
     "ACL_RULE_L2_INVALID_ETHER": {
         "desc": "Configure invalid MAC address format.",
         "eStrKey" : "Pattern"
+    },
+    "ACL_PACKET_ACTION_VALIDATE_VALUE_ACCEPT": {
+        "desc": "Configure CTRLPLANE with proper action ACCEPT."
     }
 }

src/sonic-yang-models/tests/yang_model_tests/tests_config/acl.json

@@ -789,5 +789,36 @@
                 ]
             }
         }
+    },
+    "ACL_PACKET_ACTION_VALIDATE_VALUE_ACCEPT": {
+        "sonic-acl:sonic-acl": {
+            "sonic-acl:ACL_RULE": {
+                "ACL_RULE_LIST": [
+                    {
+                        "ACL_TABLE_NAME": "SNMP_ACL",
+                        "DST_IP": "10.186.72.0/26",
+                        "IP_TYPE": "IPv4ANY",
+                        "PACKET_ACTION": "ACCEPT",
+                        "PRIORITY": 999980,
+                        "RULE_NAME": "Rule_20",
+                        "SRC_IP": "10.176.0.0/15"
+                    }
+                ]
+            },
+
+            "sonic-acl:ACL_TABLE": {
+                "ACL_TABLE_LIST": [
+                    {
+                        "ACL_TABLE_NAME": "SNMP_ACL",
+                        "policy_desc": "SNMP_ACL",
+                        "services": [
+                            "SNMP"
+                        ],
+                        "stage": "ingress",
+                        "type": "CTRLPLANE"
+                    }
+                ]
+            }
+        }
     }
 }

src/sonic-yang-models/yang-templates/sonic-types.yang.j2

@@ -61,6 +61,7 @@ module sonic-types {
     typedef packet_action{
         type enumeration {
             enum DROP;
+            enum ACCEPT;
             enum FORWARD;
             enum REDIRECT;
             enum DO_NOT_NAT;