added dockerfile for key gen

deploy/docker/key_gen/Dockerfile

@@ -0,0 +1,16 @@
+# syntax=docker/dockerfile:experimental
+FROM rust:1.70 as builder
+
+WORKDIR /app
+COPY . .
+RUN --mount=type=cache,target=/usr/local/cargo/registry \
+    --mount=type=cache,sharing=private,target=/app/target \
+	cargo build --release && \
+    # Copy executable out of the cache so it is available in the final image.
+    cp target/release/sentc_api_key_gen ./sentc_api_key_gen
+
+FROM debian:bullseye-slim
+
+COPY --from=builder /app/sentc_api_key_gen /
+
+CMD ["/sentc_api_key_gen"]