Add an API that returns the most active users and the projects where they've been active

crates/collab/migrations/20220620211403_create_project_activity_periods.sql

@@ -0,0 +1,9 @@
+CREATE TABLE IF NOT EXISTS "project_activity_periods" (
+    "id" SERIAL PRIMARY KEY,
+    "duration_millis" INTEGER NOT NULL,
+    "ended_at" TIMESTAMP NOT NULL,
+    "user_id" INTEGER REFERENCES users (id) NOT NULL,
+    "project_id" INTEGER
+);
+
+CREATE INDEX "index_project_activity_periods_on_ended_at" ON "project_activity_periods" ("ended_at");