SCD Type 2-style data sources

[tokoko]

Is your feature request related to a problem? Please describe.
Feast only supports specifying a single event_timestamp value for each row in a data source. While feast also supports expiring these values, it's managed with a single feature-view level ttl value. This is useful for a lot of use cases when feature computations might happen sporadically, but doesn't really make sense when feature computations are done as part of a periodic (daily, monthly) ETL processes or when features are already in-place in data warehouse as type 2 scd tables.

Describe the solution you'd like
Add an option to specify a column for row expiration in data sources (something like event_expire_timestamp). user will be able to specify either this column or a ttl value. offline store engines will have to handle both scenarios. in case event_expire_timestamp is provided, I think offline stores should assume that there are no overlaps, as in most scenarios users will have much easier time making sure there are no overlaps with scd type 2 tables themselves. This assumption will simplify offline store point-in-time logic quite a bit as offline store engine won't have to do additional window operations to get rid of duplicates.