Group minimum role should be Guest for work item relations
## Summary As per https://gitlab.com/groups/gitlab-org/-/epics/10266, we should reduce the minimum role to relate two records to `Guest`. This epic is to address the relationships associated with work items. ## Proposal | Relation | Description | {-Current Permissions-} | {+New Permissions+} | Status | | ------ | ------ | ------ | ------ | ------ | | Objective-Objective (vertical) | Add a child objective to an objective | `Reporter` access in both work items |`Guest` access in both work items | Scheduled with https://gitlab.com/gitlab-org/gitlab/-/issues/404795 | | Objective-Key Result (vertical) | Add a key result to an objective | `Reporter` access in both work items | `Guest` access in both work items | Scheduled with https://gitlab.com/gitlab-org/gitlab/-/issues/404796 |
epic