2ndQuadrant/pglogical REL2_4

Version 2.4.0 is a maintenance release of pglogical 2.

Changes

Add preliminary support for PostgreSQL 14 (beta)
Fix pglogical_show_subscription_table to return row rather than set of rows
Fix snapshot handling in output plugin and apply worker
Fix command quoting on Windows so that it actually works
Seems like the API used before has 1024 limit on command line length
Make sure that the schema syncing process can be interrupted on Windows
Fix compilation issues with pglogical_create_subscriber on Windows
Fix double closing of relation when a BEFORE ROW DELETE trigger returns NULL in the apply worker
Fix multi-insert crash in the SPI apply worker
Fix multi-insert doing insert of last tuple multiple times in apply worker
Make sure debug_query_string is always set
Newer versions of PostgreSQL require that debug_query_string is always set.