Support SET TIME ZONE LOCAL syntax

[TennyZhuang]

Is your feature request related to a problem? Please describe.

Currently, we've supported the following syntax to set timezone.

SET timezone TO 'Asia/Shanghai';

And PostgreSQL also supports the following syntax:

SET [ SESSION | LOCAL ] TIME ZONE { value | 'value' | LOCAL | DEFAULT }

The new syntax allow we set the timezone to the server local timezone, which is useful in testing.

Describe the solution you'd like

No response

Describe alternatives you've considered

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Additional context

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