ns8-core: cannot restore single-instance app

[Amygos]

Steps to reproduce

• Perform a backup of an app with limit 1 instance per node e.g.
  nethvoice-proxy2
• Go to the app restore section and select the desired backup
• Enable the option "Replace existing app nethvoice-proxy2"
• Proceed to the next steps
• The error "No node eligible for instance restoration" appears

Expected behavior

It should be possible to select a node and complete the restore process,
especially when choosing to replace an existing app.

Actual behavior

The process is blocked with the message "No node eligible for instance
restoration", preventing completion of the restore even though the replacement
option was selected.

Some modules are limited to a single instance per node. Even though the user
chose to replace the existing instance, the system still considers the node
ineligible.

Components

• ns8-core

See also

https://mattermost.nethesis.it/nethesis/pl/85zmwrue9irsjkphpat776hy3c

[stephdl]

This issue will be verified at #7405

[DavidePrincipi]

@mrmarkuz @stephdl can you mark this issue VERIFIED too?

[mrmarkuz]

Verified in #7405