Make it possible to have dynamic `ticket_id` range for larger exhibitions.

[Afshari9978]

Having while loop for generating random ticket_id might be expensive for large exhibitions. Solutions which I think might become handy, are:

• Defining MAX_USERS parameter in config.py file can prevent most of iterations in while loop.
• Adding a counter to while loop, & having a limit for it, we can extend random number length. With changing the start range of random.randint, it become more likely to find a new random number.