Datetime input - time zone support

## Summary
Datetime input needs to provide the ability to select a timezone

## 💬 Description
A full description of what the component or pattern should be and how it should work.

## 💰 User value
Describe why this is important and how it will help users (either developers, designers or the end-users). Think about how it makes people's lives easier, more accessible or quicker to build stuff.

## 📚 User Stories
If relevant, describe the high-level functionality as user stories.

*As an* ICDS user:
*I need*
*So that*

## 📝 Acceptance Criteria
If relevant, describe in full detail the different interactions and edge cases that the component or patterns needs to fulfil.

*Given*
*When*
*Then*

## ✏ Designs
If there's a Figma design file (or other mock-up), include it here.

## 🧾 Guidance
If there's written guidance or documentation, include a link to it here.

## Additional info
Tell us anything else useful to help us understand your suggestion.

The issue does not name a file, test, design, guidance document, or concrete acceptance criteria. Start by locating the datetime input component in the TypeScript codebase and clarify the timezone-selection behavior, supported edge cases, and expected user experience before implementation. Done is not defined until those requirements and validation steps are supplied.

Written by the indexing model from the issue text.