fix: Correct swapped metric types in Postgres deployment guide

[claudespice]

Summary

• Fix swapped metric types for replication_bootstrap_rows_total and replication_bootstrap_complete in the Postgres deployment guide metrics table.
• Per the source implementation (connector-postgres/src/replication.rs), replication_bootstrap_rows_total uses ObservableCounterU64 and replication_bootstrap_complete uses ObservableGaugeU64. The docs had these two types reversed.

Test plan

• Verify the metrics table in the Postgres deployment guide renders correctly
• Confirm metric types match the implementation in spiceai/spiceai

[github-actions]

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[github-actions]

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