[Workspace] Refactor the UI of workspace picker

[yubonluo]

Description

Refactor the UI of workspace picker

Issues Resolved

https://github.com/opensearch-project/OpenSearch-Dashboards/issues/7044

Screenshot

https://github.com/opensearch-project/OpenSearch-Dashboards/assets/71875999/61e449b5-43e8-4b4b-af08-8bb780215e6e

Testing the changes

1. Clone the latest osd code and run yarn osd bootstrap
2. Modify config/opensearch_dashboards.yml

workspace.enabled: true 

3. Run yarn start --no-base-path
4. Click workspace picker

Changelog

• feat: [Workspace] Refactor the UI of workspace picker

Check List

• [ ] All tests pass
  • [ ] yarn test:jest
  • [ ] yarn test:jest_integration
• [ ] New functionality includes testing.
• [ ] New functionality has been documented.
• [ ] Update CHANGELOG.md
• [ ] Commits are signed per the DCO using --signoff