Small fixes for Asset view until we add pagination #3274, #3261, #3154, #3286

Summary:
Add a small label identifying how data is sampled for graphs in partition mode #3274

Remove interpolation from asset graphs #3154

Exclude materializations where partition=null from partitioned graphs #3261

Double amount of data displayed to slightly aleviate need for partition-key pagination #3268

Test Plan: Run snapshot tests

Reviewers: dish, prha, sandyryza

Reviewed By: sandyryza

Differential Revision: https://dagster.phacility.com/D5298