RE: Documentation to upgrade logical replication cluster

Dear Vignesh,

Thanks for updating the patch! Here are my comments for v6.

01.
```
+ <glossterm>Logical replication cluster</glossterm>
+ <glossdef>
+ <para>
+ A set of publisher and subscriber instance with publisher instance
+ replicating changes to the subscriber instance.
+ </para>
+ </glossdef>
```

Should we say 1:N relationship is allowed?

02.
```
@@ -70,6 +70,7 @@ PostgreSQL documentation
pg_upgrade supports upgrades from 9.2.X and later to the current
major release of <productname>PostgreSQL</productname>, including snapshot and beta releases.
</para>
+
</refsect1>
```

Unnecessary blank.

03.
```
<para>
- These are the steps to perform an upgrade
- with <application>pg_upgrade</application>:
+ Below are the steps to perform an upgrade
+ with <application>pg_upgrade</application>.
</para>
```

I'm not sure it should be included in this patch.

04.
```
+ If the old primary is prior to version 17.0, then no slots on the primary
+ are copied to the new standby, so all the slots on the old standby must
+ be recreated manually.
```

I think that "all the slots on the old standby" must be created manually in any
cases. Therefore, the preposition ", so" seems not correct.

05.
```
If the old primary is version 17.0 or later, then
+ only logical slots on the primary are copied to the new standby, but
+ other slots on the old standby are not copied, so must be recreated
+ manually.
```

How about replacing this paragraph to below?

```
All the slots on the old standby must be recreated manually. If the old primary
is version 17.0 or later, then only logical slots on the primary are copied to the
new standby.
```

Best Regards,
Hayato Kuroda
FUJITSU LIMITED
https://www.fujitsu.com/