pgsql: Restrict REPACK (CONCURRENTLY) to the heap access method.

Restrict REPACK (CONCURRENTLY) to the heap access method.

REPACK (CONCURRENTLY) didn't check the table AM of the table being
repacked, so if the table AM doesn't support logical decoding, the
concurrent changes are never decoded and are silently lost from the
rewritten table.

Fix by erroring out for tables that use a non-heap access method.

Reported-by: Nathan Bossart <nathandbossart(at)gmail(dot)com>
Author: Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>
Reviewed-by: Nathan Bossart <nathandbossart(at)gmail(dot)com>
Reviewed-by: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Discussion: https://postgr.es/m/apBkixO4xAGFoiT3@nathan
Backpatch-through: 19

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/e8636f2bed258ca5be115aca33de00346d687de4

Modified Files
--------------
doc/src/sgml/ref/repack.sgml | 6 ++++++
src/backend/commands/repack.c | 14 ++++++++++++++
2 files changed, 20 insertions(+)