feat: Support SET TIME ZONE syntax

[MazterQyou]

This PR adds support for SET TIME ZONE syntax present in PostgreSQL and Redshift dialects. Related test is included.

[coveralls]

Pull Request Test Coverage Report for Build 21671163220

Details

• 31 of 35 (88.57%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.003%) to 89.508%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ast/mod.rs	9	11	81.82%
src/parser.rs	7	9	77.78%

Totals
Change from base Build 17963766437:	-0.003%
Covered Lines:	9137
Relevant Lines:	10208

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💛 - Coveralls