Update grpc-gateway and openapiv2 plugins (#902)

Update the grpc-gateway patch to enable generated SDKs to apply cleanly
to v2.18.1.

Fixes #901.

plugins/grpc-ecosystem/gateway/v2.18.1/.dockerignore

@@ -0,0 +1,3 @@
+*
+!Dockerfile
+!separate_pkg_additional_imports.patch

plugins/grpc-ecosystem/gateway/v2.18.1/Dockerfile

@@ -0,0 +1,18 @@
+# syntax=docker/dockerfile:1.4
+FROM golang:1.21.3-bullseye AS build
+
+WORKDIR /tmp
+RUN git clone --depth 1 --branch v2.18.1 https://github.com/grpc-ecosystem/grpc-gateway.git
+COPY --link separate_pkg_additional_imports.patch /tmp/separate_pkg_additional_imports.patch
+WORKDIR /tmp/grpc-gateway
+RUN git apply /tmp/separate_pkg_additional_imports.patch
+WORKDIR /tmp/grpc-gateway/protoc-gen-grpc-gateway
+RUN --mount=type=cache,target=/go/pkg/mod \
+    CGO_ENABLED=0 \
+    go build -ldflags "-s -w" -trimpath
+
+FROM scratch
+COPY --from=build --link --chown=root:root /etc/passwd /etc/passwd
+COPY --from=build --link /tmp/grpc-gateway/protoc-gen-grpc-gateway .
+USER nobody
+ENTRYPOINT [ "/protoc-gen-grpc-gateway" ]

plugins/grpc-ecosystem/gateway/v2.18.1/buf.plugin.yaml

@@ -0,0 +1,22 @@
+version: v1
+name: buf.build/grpc-ecosystem/gateway
+plugin_version: v2.18.1
+source_url: https://github.com/grpc-ecosystem/grpc-gateway
+integration_guide_url: https://github.com/grpc-ecosystem/grpc-gateway#usage
+description: gRPC to JSON proxy generator following the gRPC HTTP spec.
+output_languages:
+  - go
+registry:
+  go:
+    deps:
+      - module: github.com/grpc-ecosystem/grpc-gateway/v2
+        version: v2.18.1
+  opts:
+    - paths=source_relative
+    - standalone=true
+    - separate_package=true
+deps:
+  - plugin: buf.build/protocolbuffers/go:v1.31.0
+  - plugin: buf.build/grpc/go:v1.3.0
+spdx_license_id: BSD-3-Clause
+license_url: https://github.com/grpc-ecosystem/grpc-gateway/blob/v2.18.1/LICENSE.txt