Implement smart refresh indexes of append-only data

[apoorvedave1]

Describe the issue

Implement refresh(mode = "smart") of refresh of incremental data. The smart mode does a combination of #110 and #111 in a single step when the user calls the above api.
It uses the new unindexed data along with the small files from previous index snapshot to create a new index version.

Thanks @sezruby for suggesting this.

To Reproduce

Expected behavior

Environment