doc: Fix data checksum progress reporting documentation

doc: Fix data checksum progress reporting documentation

Add pg_stat_progress_data_checksums to the progress reporting summary
and the list of commands with progress reporting.

Also clarify that the view reports both enabling and disabling data
checksums, and correct the documented types of its progress counters
to bigint.

Author: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/CAHGQGwHJHJYAkYZBi3_O13np-Rou9UL637=hB3Y_-qdCgcZn-w@mail.gmail.com
Backpatch-through: 19