Add sqlite to backend roadmap

src/data/roadmaps/backend/content/106-relational-databases/101-sqlite.md

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+# SQLite
+
+SQLite is a relational database management system that is embedded into the end program. It is self-contained, serverless, zero-configuration, transactional SQL database engine.
+
+Visit the following resources to learn more:
+
+- [SQLite website](https://www.sqlite.org/index.html)
+- [SQLite Tutorial](https://www.sqlitetutorial.net/)