in UI, populate asset event "Source data" using event tags

[sryza]

On the "Events" tab of the asset details page, each event has a "Source data" section which contains links to upstream materializations that the event is based on.

These links are populated using a heuristic that can be inaccurate and also deviate from the materialization lineage information that we include in asset event tags.

The heuristic: look at the timestamp of the event and find the latest materialization of the upstream asset that's before that timestamp. One way this can be inaccurate is if the upstream asset was re-materialized after the downstream asset started the process of being materialized.

Events have a tag prefixed with "input_event_pointer" that encodes Dagster's best understanding of the upstream event they're derived from.

[sryza]

Related issues:

• render a materialization lineage graph #14883
• enable setting asset provenance when materializing an asset #21436