Add Tantivy ADR (#1633)

ADRs/001_tantivy.md

@@ -0,0 +1,32 @@
+# Tantivy ADR
+
+**Author**
+Marko Budiselic (github.com/gitbuda)
+
+**Status**
+APPROVED
+
+**Date**
+January 5, 2024
+
+**Problem**
+
+For some of Memgraph workloads, text search is a required feature. We don't
+want to build a new text search engine because that's not Memgraph's core
+value.
+
+**Criteria**
+
+- easy integration with our C++ codebase
+- ability to operate in-memory and on-disk
+- sufficient features (regex, full-text search, fuzzy search, aggregations over
+  text data)
+- production-ready
+
+**Decision**
+
+All known C++ libraries are not production-ready. Recent Rust libraries, in
+particular [Tantivy](https://github.com/quickwit-oss/tantivy), seem to provide
+much more features, it is production ready. The way how we'll integrate Tantivy
+into the current Memgraph codebase is via
+[cxx](https://github.com/dtolnay/cxx). **We select Tantivy.**