PR for #15313
<!-- CURSOR_SUMMARY -->
---
> [!NOTE]
> Enables importing timestamp fields that were previously filtered out.
>
> - Removes explicit exclusions of `createdAt` and `updatedAt` in
`spreadsheetImportFilterAvailableFieldMetadataItems`
> - Keeps existing constraints: only active fields, system fields
limited (except `id`), exclude `deletedAt`, and only allow `RELATION`
fields that are `MANY_TO_ONE`; sorting unchanged
>
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
a2b36e4cc0. This will update automatically
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[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->
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Co-authored-by: Félix Malfait <felix@twenty.com>