correct copy for flatten replies in configure

[marcushaddon]

trafficstars

What does this PR do?

Updates text in Configure regarding Flatten Replies to reflect new functionality

What changes to the GraphQL/Database Schema does this PR introduce?

None.

Does this PR introduce any new environment variables or feature flags?

No.

If any indexes were added, were they added to INDEXES.md?

n/a

How do I test this PR?

Navigate to admin/configure/general, and note that in the setting for Flatten Replies, references to "four" have been replaced by "eight".

How do we deploy this PR?

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