Outsource db pool creation in preparation for unit tests

crates/store/migrations/20231006125208_init.sql

@@ -0,0 +1,17 @@
+CREATE TABLE calendars (
+  id TEXT PRIMARY KEY NOT NULL,
+  name TEXT NOT NULL,
+  owner TEXT NOT NULL,
+  description TEXT,
+  color TEXT,
+  timezone TEXT NOT NULL
+);
+
+CREATE TABLE events (
+  uid TEXT NOT NULL,
+  cid TEXT NOT NULL,
+  ics TEXT NOT NULL,
+  PRIMARY KEY (cid, uid),
+  FOREIGN KEY (cid) REFERENCES calendars(id)
+);
+