Issue with DDL Parsing - Postgres

[Meadows, Eric A.]

Hello,

I am using Calcite's SqlParser, but I am running into a few issues with 
Postgres queries, namely that `PRIMARY`, `TIME`, and `ZONE` are not being 
properly parsed (raising an exception, instead).  The following code is what I 
am working with:

```java
import org.apache.calcite.sql.parser.SqlParser;
import org.apache.calcite.sql.ddl.SqlCreateTable;

…

SqlParser.Config sqlParserConfig = SqlParser
    .configBuilder()
    .setParserFactory(SqlDdlParserImpl.FACTORY)
    .build();
String sql = "CREATE TABLE \"elements_elementcomponent\" (\"id\" bigserial NOT 
NULL, \"created_at\" timestamp with time zone NOT NULL, \"updated_at\" 
timestamp with time zone NOT NULL, \"version\" double precision NOT NULL, 
\"git_sha\" varchar(60) NOT NULL, \"element_id\" bigint NULL, 
\"element_item_id\" bigint NULL, \"element_basket_id\" bigint NULL);";
SqlParser parser = SqlParser.create(sql, sqlParserConfig);
SqlCreateTable stmt = (SqlCreateTable) parser.parseQuery();
```

The following error, with the above keywords, occurs:
```java
org.apache.calcite.sql.parser.SqlParseException: Encountered "PRIMARY" at line 
1, column 69.
Was expecting one of:
    "AS" ...
    "DEFAULT" ...
    "GENERATED" ...
    ")" ...
    "," ...

                at 
org.apache.calcite.sql.parser.ddl.SqlDdlParserImpl.convertException(SqlDdlParserImpl.java:394)
                at 
org.apache.calcite.sql.parser.ddl.SqlDdlParserImpl.normalizeException(SqlDdlParserImpl.java:157)
                at 
org.apache.calcite.sql.parser.SqlParser.handleException(SqlParser.java:140)
                at 
org.apache.calcite.sql.parser.SqlParser.parseQuery(SqlParser.java:155)
                at .(#110:1)
```

I'm not sure why this would happen, because those keywords appear supported in 
[Apache Calcite - SQL language - 
Keywords](https://calcite.apache.org/docs/reference.html#keywords).

Cheers,
Eric