[lib] introduce CommunityStore spec

Summary:
This diff introduces the CommunityStore ops spec which is going to be used to process operations to the community store

Linear task: https://linear.app/comm/issue/ENG-6529/implement-community-store-spec

Depends on D11036

Test Plan: flow + functionality will be further tested in the stack

Reviewers: atul, inka, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11070