FR: don't require sample-related tables to include a participant ID column

[mbookman]

Data Explorer supports samples as an entity separate from participants. However it currently requires all tables related to samples to also include a participant ID.

Much of the time, the source data related to samples does not contain a participant ID, it contains a sample ID. The data design assumption is that there is a mapping table that maps sample IDs to participant IDs.

It is typically not difficult to add a participant id column to the sample-related tables, and it can simplify researchers code if the sample-related tables already include the participant ID, but it would be nice if Data Explorer didn't force this requirement.

[melissachang]

Note that we're already requiring one change to tables: Add columns with GCS paths.