Fix data checksum progress reporting docs

Hi,

While trying the new features in v19, I found a few documentation
issues with pg_stat_progress_data_checksums:

- pg_stat_progress_data_checksums has its own section, but is missing
   from the progress view summary table.

- The general progress reporting overview does not mention online data
   checksum operations.

- The section describes only checksum enabling, even though the view
   also reports checksum disabling.

- The progress counter columns are documented as integer, but are
   actually bigint.

The attached patch updates monitoring.sgml to address these issues.

Regards,

-- 
Fujii Masao