EXPLAIN command displays invalid `DESCRIBE [EXTENDED] <SourceId>` command

[spena]

Describe the bug
The EXPLAIN command displays an invalid statement which should be helpful to users to get more info about a stream or table.
For instance, DESCRIBE [EXTENDED] <SourceId> does not work. It should be DESCRIBE <SourceId> [EXTENDED]

Sources that this query reads from: 
-----------------------------------
SOURCE

For source description please run: DESCRIBE [EXTENDED] <SourceId>

Sinks that this query writes to: 
-----------------------------------
SINK

For sink description please run: DESCRIBE [EXTENDED] <SinkId>

[winnie-chiu]

Is this issue taken? If not, I would like to work on it.

[spena]

Go ahead @winnie-chiu and work on it. It hasn't been taken.