feat(datetime): add ionic theme styles to time label (#29829)

Issue number: internal
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## What is the current behavior?
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No `ionic` theme styles for the datetime time label

## What is the new behavior?
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this PR. -->

Adds styles to the time label for the `ionic` theme

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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screenshots of how the component looks before and after the change. -->


[Preview](https://ionic-framework-6m937m00k-ionic1.vercel.app/src/components/datetime/test/basic?ionic:theme=ionic)