Implements CREATE POLICY syntax for PostgreSQL

[git-hulk]

This PR implements part of the feature mentioned in #1404, and introduce two keywords:

• PERMISSIVE
• RESTRICTIVE

The following the syntax:

CREATE POLICY name ON table_name
    [ AS { PERMISSIVE | RESTRICTIVE } ]
    [ FOR { ALL | SELECT | INSERT | UPDATE | DELETE } ]
    [ TO { role_name | PUBLIC | CURRENT_ROLE | CURRENT_USER | SESSION_USER } [, ...] ]
    [ USING ( using_expression ) ]
    [ WITH CHECK ( check_expression ) ]

For the documentation, please refer:

https://www.postgresql.org/docs/current/sql-createpolicy.html

[coveralls]

Pull Request Test Coverage Report for Build 11013369949

Details

• 106 of 133 (79.7%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.04%) to 89.312%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ast/mod.rs	21	28	75.0%
src/parser/mod.rs	55	65	84.62%
tests/sqlparser_common.rs	30	40	75.0%

Files with Coverage Reduction	New Missed Lines	%
src/ast/mod.rs	1	82.42%

Totals
Change from base Build 10980785660:	-0.04%
Covered Lines:	29783
Relevant Lines:	33347

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💛 - Coveralls

[git-hulk]

cc @iffyio

[iffyio]

LGTM! cc @alamb

[alamb]

Thank you @git-hulk and @iffyio