Update get_ntp_servers return definition

Support returning details regarding individual NTP servers based
on openconfig models (/system/ntp/servers/server)

Author: bewing

napalm/base/base.py

@@ -921,12 +921,23 @@ def get_ntp_servers(self) -> Dict[str, models.NTPServerDict]:
         """
         Returns the NTP servers configuration as dictionary.
         The keys of the dictionary represent the IP Addresses of the servers.
-        Inner dictionaries do not have yet any available keys.
+        Inner dictionaries MAY contain information regarding per-server configuration.
 
         Example::
 
             {
-                '192.168.0.1': {},
+                '192.168.0.1':
+                {
+                    'address': '192.168.0.1',
+                    'port': 123,
+                    'version': 4,
+                    'association_type': 'SERVER',
+                    'iburst': False,
+                    'prefer': False,
+                    'network_instance': 'default',
+                    'source_address': '192.0.2.1',
+                    'key_id': -1,
+                },
                 '17.72.148.53': {},
                 '37.187.56.220': {},
                 '162.158.20.18': {}

napalm/base/models.py

@@ -232,7 +232,15 @@
 NTPServerDict = TypedDict(
     "NTPServerDict",
     {
-        # will populate it in the future wit potential keys
+        "address": str,
+        "port": int,
+        "version": int,
+        "association_type": str,
+        "iburst": bool,
+        "prefer": bool,
+        "network_instance": str,
+        "source_address": str,
+        "key_id": int,
     },
     total=False,
 )