support custom location for database persistent statefile (defaults to "capport.state" in cwd)

src/capport/config.py

@@ -23,6 +23,7 @@ class Config:
     session_timeout: int  # in seconds
     api_port: int
     controller_port: int
+    database_file: str  # empty str: disable database
     debug: bool
 
     @staticmethod
@@ -58,6 +59,7 @@ class Config:
             session_timeout=data.pop('session-timeout', 3600),
             api_port=data.pop('api-port', 8000),
             controller_port=data.pop('controller-port', 5000),
+            database_file=str(data.pop('database-file', 'capport.state')),
             debug=data.pop('debug', False)
         )
         if data: