Make system time optional in provision and restore (#105)

Typically, we want to use the current time as the system time.  With
this patch, the system time argument is made optional in provision and
restore and set to the current time if not set.

Fixes: #96

nethsm/__init__.py

@@ -540,12 +540,15 @@ def provision(
         self,
         unlock_passphrase: str,
         admin_passphrase: str,
-        system_time: Union[str, datetime],
+        system_time: Optional[Union[str, datetime]] = None,
     ) -> None:
         from .client.components.schema.provision_request_data import (
             ProvisionRequestDataDict,
         )
 
+        if system_time is None:
+            system_time = datetime.now(timezone.utc)
+
         request_body = ProvisionRequestDataDict(
             unlockPassphrase=unlock_passphrase,
             adminPassphrase=admin_passphrase,
@@ -1413,13 +1416,16 @@ def backup(self) -> bytes:
             )
         return response.response.data
 
-    def restore(self, backup: Bytes, passphrase: str, time: datetime) -> None:
+    def restore(self, backup: Bytes, passphrase: str, time: Optional[datetime]) -> None:
         try:
             from .client.components.schema.restore_request import (
                 ArgumentsDict,
                 RestoreRequestDict,
             )
 
+            if not time:
+                time = datetime.now(timezone.utc)
+
             body = RestoreRequestDict(
                 arguments=ArgumentsDict(backupPassphrase=passphrase, systemTime=time),
                 backup_file=backup,