synapse/changelog.d/15044.feature

Add two new Third Party Rules module API callbacks: [`on_add_user_third_party_identifier`](https://matrix-org.github.io/synapse/v1.79/modules/third_party_rules_callbacks.html#on_add_user_third_party_identifier) and [`on_remove_user_third_party_identifier`](https://matrix-org.github.io/synapse/v1.79/modules/third_party_rules_callbacks.html#on_remove_user_third_party_identifier).