Begin tracking follow states on collab server

Co-Authored-By: Antonio Scandurra <me@as-cii.com>

crates/collab/src/db/follower.rs

@@ -0,0 +1,51 @@
+use super::{FollowerId, ProjectId, RoomId, ServerId};
+use rpc::ConnectionId;
+use sea_orm::entity::prelude::*;
+use serde::Serialize;
+
+#[derive(Clone, Debug, Default, PartialEq, Eq, DeriveEntityModel, Serialize)]
+#[sea_orm(table_name = "followers")]
+pub struct Model {
+    #[sea_orm(primary_key)]
+    pub id: FollowerId,
+    pub room_id: RoomId,
+    pub project_id: ProjectId,
+    pub leader_connection_server_id: ServerId,
+    pub leader_connection_id: i32,
+    pub follower_connection_server_id: ServerId,
+    pub follower_connection_id: i32,
+}
+
+impl Model {
+    pub fn leader_connection(&self) -> ConnectionId {
+        ConnectionId {
+            owner_id: self.leader_connection_server_id.0 as u32,
+            id: self.leader_connection_id as u32,
+        }
+    }
+
+    pub fn follower_connection(&self) -> ConnectionId {
+        ConnectionId {
+            owner_id: self.follower_connection_server_id.0 as u32,
+            id: self.follower_connection_id as u32,
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
+pub enum Relation {
+    #[sea_orm(
+        belongs_to = "super::room::Entity",
+        from = "Column::RoomId",
+        to = "super::room::Column::Id"
+    )]
+    Room,
+}
+
+impl Related<super::room::Entity> for Entity {
+    fn to() -> RelationDef {
+        Relation::Room.def()
+    }
+}
+
+impl ActiveModelBehavior for ActiveModel {}