・Renamed the functions pg_start_backup()/pg_stop_backup() to
pg_backup_start()/pg_backup_stop() and change the arguments of pg_backup_stop()
pg_rman already supported non-exclusive mode, so we just renamed
the function names and change the arguments to keeps the behavior.

・Default log_checkpoints for regression test is off.
In PostgreSQL15, the default value of log_checkpoints is on.
The checkpoints are automatically triggered when regression tests are run.
The test failed because some log files was updated timestamp and the wrong log was deleted.
So, we turned this feature off before running the test.

* Add notes to take a backup at standby-site

* Unify 'standby site' to 'standby-site'

Co-authored-by: Masahiro Ikeda <masahiro.ikeda.us@hco.ntt.co.jp>

Previously, if the server has a tablespace and
its path has PGDATA's path, the restore
fails because mkdirs.sh doesn't work.

For example, the following case fails to restore.

* PGDATA path: /tmp/pgdata
* tablespace path: /tmp/pgdata_tblspc

So, this patch fixes the case. The root cause
is the logic checking whether the file taking backup
is in tablespace or PGDATA.

Because it only considers their prefix, if the prefix
path of tablespace is the same as PGDATA, it decides
the file is in PGDATA.

So, this patch changes the logic to check it has '/'
after the prefix.

・Renamed the functions pg_start_backup()/pg_stop_backup() to
pg_backup_start()/pg_backup_stop() and change the arguments of pg_backup_stop()
pg_rman already supported non-exclusive mode, so we just renamed
the function names and change the arguments to keeps the behavior.

・Default log_checkpoints for regression test is off.
In PostgreSQL15, the default value of log_checkpoints is on.
The checkpoints are automatically triggered when regression tests are run.
The test failed because some log files was updated timestamp and the wrong log was deleted.
So, we turned this feature off before running the test.

The following commit(17f7109) forgot to change the index of
parameters although it adds a new parameter.
It makes --hard-copy not work in restore.
And there is no test code to check that the default option uses
symbolic links. 
So add some test code and modified the manual 
about describe the -Z option.

・Renamed the functions pg_start_backup()/pg_stop_backup() to
pg_backup_start()/pg_backup_stop() and change the arguments of pg_backup_stop()
pg_rman already supported non-exclusive mode, so we just renamed
the function names and change the arguments to keeps the behavior.

・Default log_checkpoints for regression test is off.
In PostgreSQL15, the default value of log_checkpoints is on.
The checkpoints are automatically triggered when regression tests are run.
The test failed because some log files was updated timestamp and the wrong log was deleted.
So, we turned this feature off before running the test.

…nto test_pg15_bate1