Add name field to streaming audit events

As part of a the update streaming audit event UI styles (Update streaming audit event UI styles (#411005 - closed)) there is a new field to add a name to a destination. This field to help users better distinguish between destinations.

Proposal

Add a field to the streaming audit events destination form called Name

This field is required to add a destination

Design

Implementation steps

frontend

• Add GlFormInput for the name above the destination url in /audit_events/components/stream/stream_destination_editor.vue
• For creating: update addDestinationUrl() method to provide name
• For editing: update updateDestination() method to provide name
• Update requires graphql queries/mutations to accept/provide name in frontend
• This is a required field -> if no name is provided, the Add/Submit button should be disabled
• Update documentation at http://docs.gitlab.com/ee/administration/audit_event_streaming.html