Allow administrators to set days of inactivity for automatic deactivation of dormant user
<!-- This template is a great use for issues that are feature::additions or technical tasks for larger issues.--> ### Proposal <!-- Use this section to explain the feature and how it will work. It can be helpful to add technical details, design proposals, and links to related epics or issues. --> <!-- Consider adding related issues and epics to this issue. You can also reference the Feature Proposal Template (https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Feature%20proposal%20-%20detailed.md) for additional details to consider adding to this issue. Additionally, as a data oriented organization, when your feature exits planning breakdown, consider adding the `What does success look like, and how can we measure that?` section. --> Currently, we allow administrators to [enable automatic deactivation of dormant users](https://docs.gitlab.com/ee/user/admin_area/moderate_users.html#automatically-deactivate-dormant-users) (MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/62969) where it is fixed at 90 days of inactivity. This number might not be suitable for all organization. Customers should be able to customize the number of days to be considered as inactive dormant user. **NOTE:** Customer was also interested to shorten the timespan to less than 90 days. Feature requested by a Premium [Customer](https://gitlab.my.salesforce.com/0014M00001lb2JgQAI) via [Zendesk Internal ticket](https://gitlab.zendesk.com/agent/tickets/226092) ([All GitLab team member can view the ticket](https://about.gitlab.com/handbook/support/internal-support/#viewing-support-tickets))
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