feat: add wasm-rust sdk with say-hello simple extension (#350)

plugins/wasm-rust/Dockerfile

@@ -0,0 +1,12 @@
+FROM rust:1.69 as builder
+WORKDIR /workspace
+RUN rustup target add wasm32-wasi
+ARG PLUGIN_NAME="say-hello"
+ARG BUILD_OPTS="--release"
+COPY . .
+WORKDIR /workspace/extensions/$PLUGIN_NAME
+RUN cargo build --target wasm32-wasi $BUILD_OPTS \
+    && cp target/wasm32-wasi/release/*.wasm /main.wasm
+
+FROM scratch
+COPY --from=builder /main.wasm plugin.wasm