[FEATURE] Create a "Secrets" tab in the UI

### Certification

- [x] I certify I am an Epic Owner for Kubeflow Notebooks 2.0 and expected to create planning-related issues.

### Motivation

Similar to the volumes menu item in Central Dashboard, we should create a dedicated page for secrets in Notebooks 2.0, which lets users with the required Kubernetes RBAC (based on their userid-header value) do things like get/list/create new secrets.

We can also provide integration with the workspaces by showing which workspaces are mounting each secret.

### High Level Design / Mock-ups

- This new screen should rely on the Secrets API defined in #654
- `frontend` should leverage reusable component(s) from the Create/Edit Workspace wizard flow in rendering this dedicated screen
- Implements behavior similar to `GET /workspacekinds` API behavior that is "customized" for Bella vs. Joel
- #645

### Acceptance Criteria

- [ ] Users can access a dedicated 'Secrets' screen from left-hand nav
- [ ] Behavior of screen should accommodate for the "Joel" vs. "Bella" use case in terms of information returned and actions allowed
- [ ] Dedicated screen should be built upon re-usable components also leveraged in the Workspace Create/Update wizard flow

Start with the Secrets API described in #654 and the reusable components from the Create/Edit Workspace wizard flow. Trace how the frontend handles the customized /workspacekinds behavior for the Joel and Bella use cases, then connect the new screen to the left-hand navigation. Done means users can access the Secrets screen, permitted actions and returned information vary by RBAC context, and workspace mounts are shown.

Written by the indexing model from the issue text.