Add ability to select a 24-hour format as a parameter of showTimePicker

### Use case

As a Flutter developer, I often encounter scenarios where I need to provide users with the ability to select a 24-hour format based on their preferences. Currently, the showTimePicker function does not offer this capability, resulting in limitations for applications targeting diverse user bases. For instance, in international applications or those catering to specific user demographics.

### Proposal

To address this limitation and enhance the flexibility of time selection in Flutter applications, I propose adding a new parameter to the showTimePicker function that allows developers to specify the desired time format (12-hour or 24-hour). This enhancement will empower developers to tailor their applications to meet the specific needs and preferences of their user base, ultimately improving user satisfaction and usability.