[Spill To Disk][1/6] The adjustment of the basic BufferedBlockMgr includes the following change

[HappenLee]

1. Add Exec msg for BufferedBlockMgr for debug tuning
2. Change the API of Consume Memory? We will use it in HashTable in the future
3. Fix mistake of count _unfullfilled_reserved_buffers  in BufferedBlockMgr

issue:#3926

Proposed changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
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Checklist

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• I have create an issue on Doris's issues, and have described the bug/feature there in detail
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[morningman]

LGTM