Clarify the usage of the hardcoded 308 value in AttachmentPicker.tsx and AttachmentPickerError.tsx

[santhoshvai]

Motivation The hardcoded value usage of 308 in AttachmentPicker.tsx and AttachmentPickerError.tsx is unmaintanable.

308 is the default value of the prop attachmentPickerBottomSheetHeight in the OverlayProvider, so it seems like the value set in the prop must be used here.

Proposed solution Use the value of the prop in both of these components instead of the hardcoded 308.