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></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
issue