feat: add source statement to SourceDescription

[stevenpyzhang]

Description

Adds the SQL statement used to create a source to the SourceDescription object that's returned in the rest response.

This makes it easier for users to retrieve a statement for a Stream/Table in case they need to update and recreate the object. Instead of reconstructing the statement from the output of a DESCRIBE (which might not be very convenient with large schemas), they can just copy and paste it from the console/rest response.

The statement field is only present in the CLI console for EXTENDED commands.

This PR is done with the assumption that if a UPDATE/ALTER command is introduced later, getSqlExpression() would return the updated SQL statement that would be able to recreate that source. (Currently it just returns the original statement)

Testing done

Updated console tests
Spun up Server and CLI and checked the print

Name                 : FOSOD
Type                 : STREAM
Statement            : CREATE STREAM fosod(age BIGINT) WITH (KAFKA_TOPIC='foo',  VALUE_FORMAT='JSON');
Key field            : 
Key format           : STRING
Timestamp field      : Not set - using <ROWTIME>
Value format         : JSON
Kafka topic          : foo (partitions: 2, replication: 1)

 Field   | Type                      
-------------------------------------
 ROWTIME | BIGINT           (system) 
 ROWKEY  | VARCHAR(STRING)  (system) 
 AGE     | BIGINT                    
-------------------------------------

Local runtime statistics
------------------------


(Statistics of the local KSQL server interaction with the Kafka topic foo)

[
    {
        "@type": "sourceDescription",
        "statementText": "describe extended fosod;",
        "sourceDescription": {
            "name": "FOSOD",
            "readQueries": [],
            "writeQueries": [],
            "fields": [
                {
                    "name": "ROWTIME",
                    "schema": {
                        "type": "BIGINT",
                        "fields": null,
                        "memberSchema": null
                    }
                },
                {
                    "name": "ROWKEY",
                    "schema": {
                        "type": "STRING",
                        "fields": null,
                        "memberSchema": null
                    }
                },
                {
                    "name": "AGE",
                    "schema": {
                        "type": "BIGINT",
                        "fields": null,
                        "memberSchema": null
                    }
                }
            ],
            "type": "STREAM",
            "key": "",
            "timestamp": "",
            "statistics": "",
            "errorStats": "",
            "extended": true,
            "format": "JSON",
            "topic": "foo",
            "partitions": 2,
            "replication": 1,
            "statement": "CREATE STREAM fosod(age BIGINT) WITH (KAFKA_TOPIC='foo',  VALUE_FORMAT='JSON');"
        },
        "warnings": []
    }
]

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")

[big-andy-coates]

Thanks @stevenpyzhang, LGTM with the exception of the hashCode omission and the missing test.

[big-andy-coates]

needs including in hashCode as well.

This highlights the lack of testing of equals and hashCode in this class. Can you add a suitable unit test please? Take a look at our use of EqualsTester, e.g. in CreateStreamTest, for an example of the testing pattern.