[BUG] "All" dashboard should not be allowed to be deleted

[Samyak2]

Describe the bug

A default "All" dashboard is created at the time of setting up Chaos Genius or upgrading from an older version. All KPIs not assigned to any other dashboard will live here.

Deleting this dashboard causes all the KPIs inside it to be inaccessible until they are re-assigned to another dashboard.

Explain the environment

• Chaos Genius version: main (ce137b83867858e0ec1910bf1fb9e378bbad86c3)
• OS Version / Instance: Fedora 35 (applicable to all deployments)
• Deployment type: setup from scratch

Current behavior

Steps to reproduce:

• Upgrade or setup chaos genius to 0.3.0
• Enable Enterprise Edition (for dashboard feature)
• Delete option is available on the default "All" dashboard
• All dashboard is deleted successfully

Expected behavior

"All" dashboard must not have the delete option in the UI or must show an error if it's being deleted.

Screenshots

"All" dashboard deleted:

[manassolanki]

This is being handled at the backend side with a proper validation message.