Customize the solution navigation in Kibana

**What the feature is**
Customize the solution navigation in Kibana allows users to re-order or hide menu items from the left-hand solution navigation on Serverless or when solution views are enabled in ECH / on-prem.

**Value Proposition**
This feature is designed for users who need to quickly access the menu items they use most. Currently, the solution navigation can be cluttered with many applications that are irrelevant to a user's specific role, making it hard to find or discover applications they care about. By hiding unused items and placing preferred applications at the top, users can speed up their workflow and focus only on the relevant parts of the Kibana interface.

**Expected Outcome**
- A mechanism (e.g., a setting, modal, or side panel) will be introduced to allow users to configure their solution navigation.
- Hidden items will remain accessible via other means, such as the main search bar in Kibana.

**Key User Stories / Use Cases**
User Story: "As a Security Analyst, I only ever use Discover, Dashboards, and Alerts. I want to hide all other menu items (like Fleet, Maps, and Canvas) and place these applications at the very top of my navigation so I can jump straight to my core workflow every day."

User Story: "As a Developer who monitors my application with APM, I want to move the APM menu item right below Discover and hide SLOs, Synthetics, and Streams to create a cleaner workspace that only shows my performance monitoring tools."