Feature: Postgres 15 backup support

[sseekamp]

Postgres 15 changed the backup function names which causes the snapshotting function to fail with:

ERROR:  function pg_start_backup(unknown) does not exist
LINE 1: SELECT PG_START_BACKUP('zfs-auto-snapshot');
              ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
ERROR:  function pg_stop_backup() does not exist
LINE 1: SELECT PG_STOP_BACKUP();
              ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

in:

zfstools/lib/zfstools/snapshot.rb

Lines 70 to 72 in 0ac02ee

	when 'postgresql'
	sql_pre_query = "SELECT PG_START_BACKUP('zfs-auto-snapshot');"
	sql_post_query = "SELECT PG_STOP_BACKUP();"

In the docs for Postgres 15
E.4.2. Migration to Version 15
Remove long-deprecated exclusive backup mode (David Steele, Nathan Bossart)

If the database server stops abruptly while in this mode, the server could fail to start. The non-exclusive backup mode is considered superior for all purposes. Functions pg_start_backup()/pg_stop_backup() have been renamed to pg_backup_start()/pg_backup_stop(), and the functions pg_backup_start_time() and pg_is_in_backup() have been removed.

[dsampson01]

I'm running into this same issue. Would be nice to have PGSQL v15 support!