[VAULT-35044] UI: implement action buttons in updated namespace picker

[beagins]

Description

ℹ️ NOTE: This branch is merging into a feature side branch (not main)

• Implement Refresh Namespaces Button
• Implement Manage Namespaces Button
• Redirect to namespace on click
• Enterprise tests passing ✅

  236 tests completed in 171425 milliseconds, with 0 failed, 10 skipped, and 0 todo.
  1432 assertions of 1432 passed, 0 failed.

Outstanding items that will be addressed in separate PRs before the feature side branch is merged to main:

• All/Matching Namespaces Label w/ Count Badge
• "You are logged in with a root token and will have to re-authenticate when switching namespaces."
• Expanded namespace picker width to support long namespace paths
• Tab to auto-complete namespace path
• Styling to match Figma designs
• Add test coverage
• Manual testing

Screenshots

⚠️ NOTE: The current implementation looks ugly, styling will be addressed in a separate PR

TODO only if you're a HashiCorp employee

• Backport Labels: If this fix needs to be backported, use the appropriate backport/ label that matches the desired release branch. Note that in the CE repo, the latest release branch will look like backport/x.x.x, but older release branches will be backport/ent/x.x.x+ent.
  • LTS: If this fixes a critical security vulnerability or severity 1 bug, it will also need to be backported to the current LTS versions of Vault. To ensure this, use all available enterprise labels.
• ENT Breakage: If this PR either 1) removes a public function OR 2) changes the signature
  of a public function, even if that change is in a CE file, double check that
  applying the patch for this PR to the ENT repo and running tests doesn't
  break any tests. Sometimes ENT only tests rely on public functions in CE
  files.
• Jira: If this change has an associated Jira, it's referenced either
  in the PR description, commit message, or branch name.
• RFC: If this change has an associated RFC, please link it in the description.
• ENT PR: If this change has an associated ENT PR, please link it in the
  description. Also, make sure the changelog is in this PR, not in your ENT PR.

[github-actions]

CI Results:
All Go tests succeeded! ✅

[github-actions]

Build Results:
All builds succeeded! ✅

[lane-wetmore]

Left a few comments/questions, but these could be addressed in the next PR if you like.