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

[JoeyStk]

Was moved as we're not sure at the moment how sensible this issue really is. TODO for 25Q2: Reevaluate if this issue still makes sense and either plan or close it.
Alternative: Think about whether or not it makes sense to extend the "search and replace" functionality with RegEx