Evaluate name prefix policy for multi / Citus

We currently use multi as a prefix in code segments where distributed planning and execution is involved. We use the Citus prefix for nodes. It may be worth spending fifteen minutes to see if we'd like to have some policy in the future.

No file or test is named. Search code segments using the multi prefix and node-related Citus prefix, compare their roles in distributed planning and execution, and finish by recording an agreed naming policy or the decision not to create one.

Written by the indexing model from the issue text.