Add FAQ entry about enabling incremental logging (required when using object storage)

What does this MR do?

This MR updates the installing GitLab on AWS doc to add an FAQ entry letting people know that they should enable incremental logging since it's required when using object storage.

In the Amazon S3 object storage section we link to the page that notes that incremental logging is required. This FAQ entry is intended to help people who may miss that note and is inspired by a 🎫 ticket that GitLab team members with access to ZenDesk can review.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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