Change Promote to leader action icon

[DavidePrincipi]

To avoid using the same icon for both node promotion action and Subscription page, the action icon must be changed.

Proposal:

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Discussion https://mattermost.nethesis.it/nethesis/pl/1m6438b53p85ux7dobgpf93mxr

[DavidePrincipi]

Released https://github.com/NethServer/ns8-core/releases/tag/3.4.6