Contribute terms to ForgeFed

• forge:fork example https://codeberg.org/ForgeFed/ForgeFed/pulls/133 / https://codeberg.org/ForgeFed/ForgeFed/issues/145
• forge:forkedFrom https://codeberg.org/ForgeFed/ForgeFed/pulls/134
• forge:mirrors/forge:mirroredBy/forge:mirrorsTo/forge:mirroredFrom https://codeberg.org/ForgeFed/ForgeFed/pulls/148

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Migrated from T4354 (view on Phabricator)