Add target-tables argument

[FoGhost]

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WHAT

• Support target-tables flag

WHY

• We are using the same sql schema file to manage table definitions, but sometimes we want to use a different template to generate Go codes for a specific table.
• Yo already supported ignore-tables flag which can also be used for this purpose, but it's too complicated to use when there are too many tables defined in the same ddl file.

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