pgsql: Report progress of COPY commands

Report progress of COPY commands

This commit introduces a view pg_stat_progress_copy, reporting progress
of COPY commands. This allows rough estimates how far a running COPY
progressed, with the caveat that the total number of bytes may not be
available in some cases (e.g. when the input comes from the client).

Author: Josef Šimánek
Reviewed-by: Fujii Masao, Bharath Rupireddy, Vignesh C, Matthias van de Meent
Discussion: https://postgr.es/m/CAFp7QwqMGEi4OyyaLEK9DR0+E+oK3UtA4bEjDVCa4bNkwUY2PQ@mail.gmail.com
Discussion: https://postgr.es/m/CAFp7Qwr6_FmRM6pCO0x_a0mymOfX_Gg+FEKet4XaTGSW=LitKQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8a4f618e7ae3cb11b0b37d0f06f05c8ff905833f

Modified Files
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doc/src/sgml/monitoring.sgml | 107 +++++++++++++++++++++++++++++++
src/backend/catalog/system_views.sql | 11 ++++
src/backend/commands/copyfrom.c | 17 ++++-
src/backend/commands/copyfromparse.c | 4 ++
src/backend/commands/copyto.c | 22 ++++++-
src/backend/utils/adt/pgstatfuncs.c | 2 +
src/include/commands/copyfrom_internal.h | 1 +
src/include/commands/progress.h | 5 ++
src/include/pgstat.h | 3 +-
src/test/regress/expected/rules.out | 9 +++
10 files changed, 176 insertions(+), 5 deletions(-)