fix: Correct ScyllaDB connector filter pushdown docs

[claudespice]

Summary

• The ScyllaDB connector docs incorrectly stated that filter pushdown was entirely disabled. The actual implementation pushes down partition key equality (=) and clustering key comparison (=, <, <=, >, >=) filters to CQL.
• Replaced the "Why Filter Pushdown is Disabled" section with an accurate "Filter Pushdown" section describing Exact (partition key) and Inexact (clustering key) pushdown behavior, plus a table of what is/isn't pushed down.
• Removed misleading "by default" from the batch size description (8192 is hardcoded, not configurable).
• Updated the Performance Considerations section to note that partition/clustering key filters reduce data transfer.
• Updated the CQL Limitations section to accurately describe which WHERE clause filters are pushed down.
• Applied the same fix to both website/docs/ (vNext) and website/versioned_docs/version-1.11.x/.

Test plan

• Verify the vNext ScyllaDB docs page renders correctly with the new filter pushdown table
• Verify the v1.11.x ScyllaDB docs page renders correctly with the same changes
• Confirm no other sections (params, types, examples) were modified

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