support analyze for unionstore table in cloudberry

[gongxun0928]

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Change logs

1. support non-dispatch analyze operation for custom table am in cloudberry.
2. added a void *context parameter to scan_begin to pass some additional parameters

Why are the changes needed?

we want to support custom table am to support analyze operations without modifying the kernel every time

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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