[Feature] Move more metadata into the project level

At the moment we store everything at the individual array level (in the proposal). We should consider moving more data into the overarching project level.

Start by reviewing the proposal and mapping which metadata is currently stored at the individual array level. Clarify which fields belong at the project level, document the resulting model, and confirm the API behavior and tests that should define completion.

Written by the indexing model from the issue text.