fix(storage): use per-table committed epoch in read version update

[wenym1]

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What's changed and what's your intention?

In HummockReadVersion update, we still use the global max committed epoch. In this PR we will change to use the per table committed epoch

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[hzxa21]

Rest LGTM

[hzxa21]

In which case will these two be None?

[wenym1]

Previously, when an empty WatermarkIndex is created, the latest_epoch is None, but now I just realize that the latest_epoch can always be Some(_), because all WatermarkIndex::new is followed by a add_epoch_watermark, so I change the new method to create the WatermarkIndex together with the first watermark, and then the latest_epoch can always be Some(_) and we can remove the Option.

The committed_epoch is None when a new watermark is written, but no data has ever been committed for this table, so the committed_epoch of this table id is None.