Backend tries to host API on port 5000 but `compose.yaml` doesn't forward 5000

[SuitablyMysterious]

I am checking that these endpoints exist:

@SuitablyMysterious ➜ /workspaces/Library-System (dev) $ curl -X GET http://localhost:8000/Book/getByISBN
curl: (56) Recv failure: Connection reset by peer

@SuitablyMysterious ➜ /workspaces/Library-System (dev) $ curl -X GET http://localhost:5000/Book/getByName
curl: (7) Failed to connect to localhost port 5000 after 0 ms: Couldn't connect to server

[SuitablyMysterious]

Part of #141