Allow IR nodes to use multiple collective IDs

[rjzamora]

Description

Relaxes the current restriction that a single IR node can only use a single collective ID. We will need some IR nodes (e.g. Join) to use multiple collectives when partitioning decisions are made dynamically.

Blocker for dynamic planning.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.