[minor][cdc-connector][mongodb] Add `op_type` metadata column

[qg-lin]

Add op_type metadata column for mongodb source connector

[qg-lin]

@Jiabao-Sun @yuxiqian PTAL

[qg-lin]

Since DeduplicateFunctionHelper#processLastRowOnChangelog returns the row before deletion, the delete type is temporarily missing.

[github-actions[bot]]

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[github-actions[bot]]

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