historian: avoid leaving db lock in place when shutting down

Avoid the error:
plugin-historian.py: sqlite3.OperationalError: database is locked

Author: endothermicdev

archived/historian/historian.py

@@ -309,10 +309,10 @@ def publish(self, raw: bytes) -> None:
 @plugin.init()
 def init(plugin, configuration, options):
     print(options)
-    engine = create_engine(options['historian-dsn'], echo=False)
-    Base.metadata.create_all(engine)
-    plugin.engine = engine
-    Flusher(engine).start()
+    with create_engine(options['historian-dsn'], echo=False) as engine:
+        Base.metadata.create_all(engine)
+        plugin.engine = engine
+        Flusher(engine).start()
 
 
 @plugin.method('historian-stats')