feat: option to return only new records when calling `GetRewardsByAvsForDistributionRoot`

[seanmcgary]

Currently GetRewardsByAvsForDistributionRoot returns ALL rewards data for the provided rootIndex.

We should add a request parameter to return only the net new rewards snapshot row for the provided root index since the previous valid root (i.e. if rootIndex - 1 was disabled, find the next closest non-disabled root).