Add new column "Regions" to broken link list of network management

[MizukiTemma]

Motivation

Centralised link management system is introduced by #2971 but one thing is still missing: number of regions that are affected by the link.

Proposed Solution

Add a new column "Regions" to the link list in the network management and show how many regions are using the URL.

Alternatives

Leave it not implemented 😿

User Story

Additional Context

Design Requirements