Mention same file storage method requirement for Geo

What does this MR do?

Adds a clearer note that the storage method on Geo secondaries needs to match the one of the primary (i.e. using object storage on both, or local storage on both)

Related issues

omnibus-gitlab#6271 (closed)

Author's checklist

• Follow the Documentation Guidelines and Style Guide.
• Ensure that the product tier badge is added to doc's h1.
• Request a review based on the documentation page's metadata and associated Technical Writer.

To avoid having this MR be added to code verification QA issues, don't add these labels: feature, frontend, backend, ~"bug", or database

Review checklist

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