chore(backfill): add logging for backfill script

[christopherlim98]

Problem

There is currently no indication of progress when running the backfill script.

Closes #946

Solution

Add logging statements for each stage (i.e. querying from database, creating searchEntriesDataset, indexing the dataset on open search).

As the indexing process itself is done as a bulk operation, it is not very feasible to add a progress bar to track the progress of indexing.

Improvements:

Note: running npx ts-node search-backfill-trigger has a noticeable startup/compilation time as ts-node does type-checking in the background. In production, a faster alternative could be to add a transpile-only flag like npx ts-node -T search-backfill-trigger.

Screenshots

[wanlingt]

lgtm!