[FE] Add dormant member Group setting
# Background
In https://gitlab.com/groups/gitlab-org/-/epics/7533+ we intend to add a feature to identify and remove dormant users from Namespaces for GitLab.com
This is similar to the existing SM feature ( https://gitlab.com/groups/gitlab-org/-/epics/5519), but rather than deactivating users, we will remove members.
To achieve this, we will be adding a way to track member’s last activity timestamp within a namespace, so that we can identify dormant members and remove them if they've been dormant for greater than a predefined time period (e.g. 90 days).
# Purpose
The purpose of this issue is to:
**Add frontend form changes for updating group setting**
The backend changes will be handled in:
- https://gitlab.com/gitlab-org/gitlab/-/issues/461334+
- https://gitlab.com/gitlab-org/gitlab/-/issues/461335+
We can develop this behind a feature flag before the related work is complete
## Implementation
* Backend: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/153099+
* Frontend: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/153118+
issue