Migrate "batch strategy" enum to lookup table

[maxachis]

Currently, batches.batch_strategy exists as an enum, which must be manually updated every time a new collector is added.

This is often considered an antipattern, with the preferred approach being to develop a lookup table, perhaps batch_strategy, and batches.batch_strategy to batches.batch_strategy_id.

This way, it is trivial to add or remove another strategy, rather than having to develop a whole new enum.