Datetime picker - time zone support

## Summary
Datetime picker 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
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## 🧾 Guidance
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## Additional info
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No file, test, design, guidance, or acceptance criteria is provided. Start by locating the datetime picker component and clarifying the intended timezone-selection behavior, supported edge cases, and user value. The work is done when those requirements are implemented and verified by appropriate component tests.

Written by the indexing model from the issue text.