Add client-side validation (min/max for string and number options)

[hyperneutrino]

Summary of Changes

• added client-side validation options for string and number options (min/max length or value)

Motivation and Explanation

• certain command options such as ban purge duration (not applicable after improve ban command input #528 in this case) allow invalid inputs and only detect the error afterwards
• this change adds client-side validation to improve the user experience and understanding

Demonstration of Changes

Further Information and Comments

• this change just sets up the infrastructure. a future change can actually add this usage to any relevant commands (Use client-side validation infrastructure for applicable commands #529)