feat: cleanup docker setup

- Add .dockerignore
- Replace .env with .env.example
- Add migrations service
- Cleanup Dockerfile: simpler setup, simpler copy, no migrations inside the image
- Update README to match new instruction

.env.example

@@ -0,0 +1,11 @@
+# Environment variables declared in this file are automatically made available to Prisma.
+# See the documentation for more detail: https://pris.ly/d/prisma-schema#accessing-environment-variables-from-the-schema
+
+# Prisma supports the native connection string format for PostgreSQL, MySQL, SQLite, SQL Server, MongoDB and CockroachDB.
+# See the documentation for all the connection string options: https://pris.ly/d/connection-strings
+
+# Enable to use different location for dev db file
+# DATABASE_URL="file:./dev.db"
+
+# Add your admin Nostr npub
+# ADMIN_NPUBS=npub1q2s369...