fix: Use deepcopy when rendering alert data in keep_provider

[StevenReitsma]

Closes #5171

📑 Description

When using the Keep provider to create alerts in a foreach loop, all generated alerts may end up sharing the same (often last) data, especially if the alert template contains nested structures (such as dictionaries or lists). Replace the shallow copy with a deep copy to ensure that each alert in the loop gets a fully independent copy of the template, including all nested structures.

Thanks to @akipham15 for the research in #5171

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