Add workspace list sorting dropdown with recent activity filter
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MR: Pending
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## Description
As part of our [new designs for Workspaces](https://gitlab.com/groups/gitlab-org/-/epics/18674), we want to give our users the ability to sort their workspace list so that they can quickly find the workspaces they want to work on.
## Acceptance criteria
- [ ] Add a dropdown filter which allows the user to select which property to sort on (_default: Recent activity_)
- [ ] Implement sort direction controls (ascending/descending) next to the dropdown
- [ ] GraphQL API call (userWorkspacesTabList) takes into account the current sort property & direction
- [ ] Loading states are handled appropriately during sort operations
- [ ] Sort preference persists within the user session
## TODO: Implementation plan
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