Allow instance admins to create shared Kubernetes agents for workspaces across multiple top-level groups
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## Problem
Currently, Kubernetes GitLab agents for workspaces are scoped to individual top-level groups. Instance admins cannot create a single agent that is available and usable across multiple top-level groups.
Each top-level group must create and manage their own agent configuration, leading to:
- Duplicate agent configurations across groups
- Increased operational overhead for managing multiple agent instances
- Complexity in managing workspace infrastructure across organizational units
## Proposed Solution
Allow instance admins to create and manage shared Kubernetes agents at the instance level that can be used by multiple top-level groups for workspace creation.
This would enable:
- A single agent configuration that serves multiple top-level groups
- Simplified agent management for organizations with multiple top-level groups
- Reduced duplication of agent setup and configuration
## Use Case
An organization with multiple top-level groups (e.g., different departments or business units) wants to use a single Kubernetes agent for workspaces without requiring each group to maintain separate agent configurations.
issue