Add the ability to add sequential approvals for merge requests
<!-- This template is a great use for issues that are feature::additions or technical tasks for larger issues.--> This feature proposal was created on behalf of a ~"GitLab Ultimate" [customer](https://gitlab.lightning.force.com/lightning/r/Account/0018X00003Hs79iQAB/view) (internal link) who requested this functionality in a [support ticket](https://gitlab.zendesk.com/agent/tickets/682595) (internal link) ### Proposal Currently, if there are multiple approval rules on a merge request, they operate in parallel, and there is no sequencing in approvals. It would be beneficial to configure sequential approvals, where a second approval rule is prompted for approval only after the first approval rule has been approved. Example: ``` Approval Rule 1 0 of 3 approvals Approval Rule 2 Pending Approval Rule 1 ``` <!-- Label reminders Use the following resources to find the appropriate labels: - Use only one tier label choosing the lowest tier this is intended for - https://gitlab.com/gitlab-org/gitlab/-/labels - https://about.gitlab.com/handbook/product/categories/features/ -->
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