api: only open database connection while handling requests

Helps with recovery when database restarts during long-held connections.

Code from https://docs.peewee-orm.com/en/3.15.3/peewee/database.html#flask

src/api.py

@@ -20,6 +20,19 @@ else:
 
 app = Flask(__name__)
 
+# This hook ensures that a connection is opened to handle any queries
+# generated by the request.
+@app.before_request
+def _db_connect():
+    db.connect()
+
+# This hook ensures that the connection is closed when we've finished
+# processing the request.
+@app.teardown_request
+def _db_close(exc):
+    if not db.is_closed():
+        db.close()
+
 @app.route('/', methods=['GET'])
 def root():
     query = PPETable.select() #.where(PPETable.is_active == True)