Add fn support_group_by_expr to Dialect trait

[jdye64]

This closes: #895

[coveralls]

Pull Request Test Coverage Report for Build 5260946891

• 5 of 9 (55.56%) changed or added relevant lines in 5 files are covered.
• 140 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.06%) to 86.942%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/dialect/duckdb.rs	1	2	50.0%
src/dialect/generic.rs	1	2	50.0%
src/dialect/mod.rs	1	2	50.0%
src/dialect/postgresql.rs	1	2	50.0%

Files with Coverage Reduction	New Missed Lines	%
src/lib.rs	140	11.74%

Totals
Change from base Build 5210390017:	-0.06%
Covered Lines:	14874
Relevant Lines:	17108

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💛 - Coveralls

[andygrove]

LGTM

[andygrove]

cc @jimexist @alamb

[alamb]

Thank you @jdye64