renames methods in the group handler interface to replace the channel-specific vocabulary with the more standard and generic "containers" and "items" naming conventions. --- #### Does this PR need a docs update or release note? - [x] ⛔ No #### Type of change - [x] 🧹 Tech Debt/Cleanup #### Test Plan - [x] ⚡ Unit test - [x] 💚 E2E