RE: Enhance 'pg_createsubscriber' to retrieve databases automatically when no database is provided.

Dear Shubham,

> The attached patches contain the suggested changes.

Thanks for updating the patch. I reviewed only 0001 because they would be committed separately.
Few comments:

01.
```
+ For every non-template database on the source server, create one
+ subscription on the target server in the database with the same name.
```

It is quite confusing for me; We do not have to describe users that this command
checks databases of the source server. How about something like:
"Create one subscription per all non-template databases on the target server."

02.
```
+# run pg_createsubscriber with '--database' and '--all' without '--dry-run'
+# and verify the failure
+command_fails_like(
+ [
+ 'pg_createsubscriber',
+ '--verbose',
+ '--pgdata' => $node_s->data_dir,
+ '--publisher-server' => $node_p->connstr($db1),
+ '--socketdir' => $node_s->host,
+ '--subscriber-port' => $node_s->port,
+ '--database' => $db1,
+ '--all',
+ ],
+ qr/--database cannot be used with --all/,
+ 'fail if --database is used with --all');
+
+# run pg_createsubscriber with '--publication' and '--all' and verify
+# the failure
+command_fails_like(
+ [
+ 'pg_createsubscriber',
+ '--verbose',
+ '--dry-run',
+ '--pgdata' => $node_s->data_dir,
+ '--publisher-server' => $node_p->connstr($db1),
+ '--socketdir' => $node_s->host,
+ '--subscriber-port' => $node_s->port,
+ '--all',
+ '--publication' => 'pub1',
+ ],
+ qr/--publication cannot be used with --all/,
+ 'fail if --publication is used with --all');
```

You seemed to move most of validation checks to 0002. Can you tell me a reason
why they are remained?

03.
```
+# Verify that the required logical replication objects are created. The
+# expected count 3 refers to postgres, $db1 and $db2 databases.
```

Hmm, but since we did a dry-run, any objects are not created, right?

Best regards,
Hayato Kuroda
FUJITSU LIMITED