Feature/add ext dml init fini hook for custom table am

[gongxun0928]

closes: #ISSUE_Number

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Change logs

Two hook functions , ext_dml_init_hook and ext_dml_finish_hook have been added. These functions perform some resource initialization and cleanup at the start and end of data modification operations (such as modifyTable, CopyFrom, CreateAs, Matview, etc.).

Why are the changes needed?

we have implemented some custom table am to support custom catalog services and storage formats, we need to support custom storage formats just like the ao_row/ao_co table. So we added two hook functions like appendonly_dml_init/appendonly_dml_finish

Does this PR introduce any user-facing change?

If yes, please clarify the previous behavior and the change this PR proposes.

How was this patch tested?

Please detail how the changes were tested, including manual tests and any relevant unit or integration tests.

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[github-actions]

Hiiii, @gongxun0928 welcome!🎊 Thanks for taking the effort to make our project better! 🙌 Keep making such awesome contributions!