doc: make ref/*.sgml file header comment layout consistent

Files

Documentation touched

• doc/src/sgml/ref/checkpoint.sgml
• doc/src/sgml/ref/create_cast.sgml
• doc/src/sgml/ref/create_collation.sgml
• doc/src/sgml/ref/create_conversion.sgml
• doc/src/sgml/ref/create_foreign_table.sgml
• doc/src/sgml/ref/create_function.sgml
• doc/src/sgml/ref/create_transform.sgml
• doc/src/sgml/ref/drop_cast.sgml
• doc/src/sgml/ref/drop_collation.sgml
• doc/src/sgml/ref/drop_conversion.sgml
• doc/src/sgml/ref/drop_foreign_table.sgml
• doc/src/sgml/ref/drop_transform.sgml
• doc/src/sgml/ref/load.sgml
• doc/src/sgml/ref/pg_config-ref.sgml
• doc/src/sgml/ref/pg_restore.sgml
• doc/src/sgml/ref/pgarchivecleanup.sgml
• doc/src/sgml/ref/pgbench.sgml
• doc/src/sgml/ref/pgtestfsync.sgml
• doc/src/sgml/ref/pgtesttiming.sgml
• doc/src/sgml/ref/pgupgrade.sgml
• doc/src/sgml/ref/set_constraints.sgml
• doc/src/sgml/ref/set_session_auth.sgml
• doc/src/sgml/ref/set_transaction.sgml