Add NuRaft ADR (#1634)

Co-authored-by: Andi <andi8647@gmail.com>

ADRs/002_nuraft.md

@@ -0,0 +1,34 @@
+# NuRaft ADR
+
+**Author**
+Marko Budiselic (github.com/gitbuda)
+
+**Status**
+PROPOSED
+
+**Date**
+January 10, 2024
+
+**Problem**
+
+In order to enhance Memgraph to have High Availability features as requested by
+customers, we want to have reliable coordinators backed by RAFT consensus algorithm. Implementing
+RAFT to be correct and performant is a very challenging task. Skillful Memgraph
+engineers already tried 3 times and failed to deliver in a reasonable timeframe
+all three times (approximately 4 person-weeks of engineering work each time).
+
+**Criteria**
+
+- easy integration with our C++ codebase
+- heavily tested in production environments
+- implementation of performance optimizations on top of the canonical Raft
+  implementation
+
+**Decision**
+
+There are a few, robust C++ implementations of Raft but as a part of other
+projects or bigger libraries. **We select
+[NuRaft](https://github.com/eBay/NuRaft)** because it focuses on delivering
+Raft without bloatware, and it's used by
+[Clickhouse](https://github.com/ClickHouse/ClickHouse) (an comparable peer to
+Memgraph, a very well-established product).