[lib] Don't prune messages from thick threads

Summary:
Prune messages only from Redux. It is achieved by generating DB ops only for thin threads.

https://linear.app/comm/issue/ENG-9037/old-messages-in-thick-threads-arent-loading-on-web
https://linear.app/comm/issue/ENG-8700/dont-create-ops-when-pruning-dm-messages

Test Plan: Create a thick thread with 100 messages. Refresh the web app - which causes pruning. Refresh it once again - only 20 messages should be displayed in the UI. Check if setClientDBStoreActionType action payload contains all 100 messages.

Reviewers: kamil, inka

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13106