feat(core-api): add weaver protobuf codegen hyperledger-cacti#1556

Rust code now gets generated from the Weaver protocol buffer definitions
Next step is to have the automated publishing set up.

To test the rust build, you need to run either one of the following:

`yarn lerna run proto:protoc-gen-rust` (from the project root)

or a regular cargo build from the core-api package directory, e.g.:

```sh
cd packages/cactus-core-api/
cargo build
```

Fixes hyperledger-cacti#1556

Signed-off-by: Peter Somogyvari <peter.somogyvari@accenture.com>

.gitignore

@@ -1,6 +1,7 @@
 .config.json
 .nyc_output/
 dist/
+target/
 .DS_Store
 node_modules/
 docs/main