feat: datetime, customize how "today" is calculated with grid buttons

### Prerequisites

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- [X] I agree to follow the [Code of Conduct](https://ionicframework.com/code-of-conduct).
- [X] I have searched for [existing issues](https://github.com/ionic-team/ionic-framework/issues) that already include this feature request, without success.

### Describe the Feature Request

If user has custom timezone (not the same as on device) we dont have ability to highlight the current day due to that timezone today

### Describe the Use Case

We need a property "timezone" which will render current date due to that timezone. It could be passed as UTC offset in minutes with negative or positive value. and based on that calendar will render proper current date

### Describe Preferred Solution

_No response_

### Describe Alternatives

_No response_

### Related Code

_No response_

### Additional Information

_No response_