Compile zoekt-indexer with knowledge graph Rust lib

With #89 (closed) done, we use FFI to call knowledge graph indexing (Rust lib).

To be able to do this FFI call, we should make sure that zoekt-indexer is compiled and distributed with this this knowledge graph Rust lib included:

• update zoekt-indexer build process to compile with this lib
• make sure that a stable version of knowledge graph lib is used