[fix] [doc] add plugin name into the demo of debezium-postgres-source

[poorbarcode]

The config(Example of PostgreSQL -> Configuration) demo of debezium-postgres-source contains the prop plugin.name

But in the section Example of PostgreSQL -> Usage -> Start the Pulsar Debezium connector in local run mode using one of the following methods, the prop plugin.name is missing.

• doc
• doc-required
• doc-not-needed
• doc-complete

[Anonymitaet]

Is plugin.name required?

[poorbarcode]

@Anonymitaet

Is plugin.name required?

In the demo it should be. Because not setting this parameter will throw an exception no plugin installed.(I am not sure if pgoutput is a built-in plugin that doesn't require additional installation, so it doesn't throw errors)

[Anonymitaet]

ping @shibd @nlu90 to review it, thanks!