Implement helm handlers and add configuration values to FleetAddonConfig to set up the fleet installation.

[Danil-Grigorev]

We need to implement Helm CLI wrapper, which would provide basic functionality for fleet CRD, agent and controller operations, like:

• Helm repo operation
• Helm list
• Helm install
• Helm template
• Helm uninstall

The CLI will be available in the addon image, and it will use in-cluster kubeconfig. RBAC roles should updated accordingly to allow performing operations like helm install and helm uninstall.