Add Friendica, Bluesky, Nostr icons.
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## Icon Request

* Icon name: Friendica
* Tags of this icon: will be used on elk.zone (see https://github.com/elk-zone/elk/issues/2472 )
* Use case: will be used on elk.zone (see https://github.com/elk-zone/elk/issues/2472 )
* Screenshots of similar icons: don't have anything.

## Icon Request

* Icon name: Bluesky
* Tags of this icon: will be used on elk.zone (see https://github.com/elk-zone/elk/issues/2472 )
* Use case: will be used on elk.zone (see https://github.com/elk-zone/elk/issues/2472 )
* Screenshots of similar icons: don't have anything.

## Icon Request

* Icon name: Nostr
* Tags of this icon: will be used on elk.zone (see https://github.com/elk-zone/elk/issues/2472 )
* Use case: will be used on elk.zone (see https://github.com/elk-zone/elk/issues/2472 )
* Screenshots of similar icons: don't have anything.