Move column definitions for data nodes table to the backend.

[linuspahl]

Description

Currently the column definitions for the data nodes table on /system/datanodes are hard coded in the UI.

  { id: 'hostname', title: 'Name', sortable: true },
  { id: 'transport_address', title: 'Transport address' },
  { id: 'status', title: 'Status', sortable: false },
  { id: 'cert_valid_until', title: 'Certificate valid until', sortable: false },

Usually these information come from the backend, in this case from the following request: /api/system/cluster/datanodes

The response already contains one column, which also exists in the collection above.

Ideally we remove the hard coded columns in the UI and generate these columns definition in the backend.

• Graylog Version: 6.0