feat: a missing license can say what the device withholds without it (4.15.0)

LicenseDict gets withholds: NotRequired[List[str]]: what a device keeps back
for want of a license while the rest of it answers. A Supermicro X10 with
only SFT-OOB-LIC answers Redfish but withholds its drives and firmware
inventory until DCMS is activated. That makes it partly licensed, not
unlicensed, and the caller can tell the two apart (NetOrk/netork#1111).

napalm_device_types/licenses.py

@@ -22,6 +22,11 @@ class LicenseMixin:
             Example::
 
                 [{"name": "pve-subscription", "status": "none"},
-                 {"name": "vSphere", "status": "active", "edition": "Free"}]
+                 {"name": "vSphere", "status": "active", "edition": "Free"},
+                 {"name": "DCMS", "status": "missing",
+                  "withholds": ["drives", "firmware inventory"]}]
+
+            ``withholds`` names what a device keeps back for want of a license while
+            the rest of it answers; a missing license without it may keep back all.
             """
             ...

napalm_device_types/models.py

@@ -1008,6 +1008,11 @@ class LicenseDict(TypedDict):
     edition: NotRequired[str]  # the edition or level, e.g. "Free", "Enterprise Plus"
     expires: NotRequired[Optional[str]]  # ISO date, None for no expiry
     detail: NotRequired[str]  # the device's own words, e.g. why a feature is refused
+    # What the device withholds without it while the rest works, e.g. ["drives",
+    # "firmware inventory"] on a BMC that answers but wants a further license.
+    # Absent: the device says nothing of the kind, or withholds everything it
+    # would offer with it.
+    withholds: NotRequired[List[str]]
 
 
 class HypervisorHostDict(TypedDict):