feat: tokenization start, waitlist for background task graceful exit

projects/greenlight/migrations/000005_create_tokens_table.down.sql

@@ -0,0 +1 @@
+DROP TABLE IF EXISTS tokens;

projects/greenlight/migrations/000005_create_tokens_table.up.sql

@@ -0,0 +1,7 @@
+CREATE TABLE IF NOT EXISTS tokens (
+    hash bytea PRIMARY KEY,
+    user_id bigint NOT NULL REFERENCES users ON DELETE CASCADE,
+    expiry timestamp(0) with time zone NOT NULL,
+    scope text NOT NULL
+);
+