Add a way to filter/search for a namespace
### Problem For accounts that have more than 20+ namespaces, it becomes more cumbersome to find the correct namespace. <details><summary>Current state</summary>![Screen_Shot_2021-03-11_at_17.49.21](/uploads/e1fa191e53d528ecba23c9888363324d/Screen_Shot_2021-03-11_at_17.49.21.png)</details> ### Proposal Add a way to filter / search namespaces as see in: https://gitlab.com/gitlab-org/gitlab/-/issues/13020/designs/first-run-select-namespace.png
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