wireguard: add instances column to peer tab overview

[fichtner]

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Is your feature request related to a problem? Please describe.

Working with the peer tab for feature parity seeing which instances are linked would be helpful but for now you have to edit and see or switch to instances tab, which is suboptimal if you want to quickly check assigned instances for a peer.

Describe the solution you like

Add the instances column in the peer tab.

Describe alternatives you considered

N/A because this is mostly UX / cosmetics.

Additional context

N/A