Add support for ClickHouse DDL query syntax (on cluster)

[andyrichardson]

Add support for ClickHouse DDL query syntax (source)

This is an example only on CREATE TABLE statements. If you're happy to go ahead with supporting this, I can add this to all CREATE DROP ALTER and RENAME queries

[alamb]

Looks great -- thank you @andyrichardson. I think adding support for other DDL statements sounds like a great idea.

The only possible thing that might be worth considering is to only parse ON CLUSTER when using the generic and ClickHouse dialects

[coveralls]

Pull Request Test Coverage Report for Build 2755925293

• 20 of 25 (80.0%) changed or added relevant lines in 3 files are covered.
• 741 unchanged lines in 7 files lost coverage.
• Overall coverage increased (+0.1%) to 89.916%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ast/mod.rs	3	5	60.0%
src/parser.rs	10	13	76.92%

Files with Coverage Reduction	New Missed Lines	%
tests/sqlparser_mysql.rs	1	99.8%
tests/sqlparser_postgres.rs	8	97.82%
src/ast/query.rs	17	86.61%
tests/sqlparser_common.rs	67	97.21%
src/tokenizer.rs	72	89.27%
src/ast/mod.rs	205	78.75%
src/parser.rs	371	83.37%

Totals
Change from base Build 2535757386:	0.1%
Covered Lines:	9015
Relevant Lines:	10026

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💛 - Coveralls