Add initial implementation of gitea-mcp-forward-auth microservice

- Create build and release workflows for CI/CD
- Implement Dockerfile for multi-stage builds
- Add core authentication logic with token validation
- Include HTTP handler for authorization checks
- Set up Kubernetes deployment and service manifests
- Update README with usage instructions and configuration details

Dockerfile

@@ -0,0 +1,22 @@
+ARG GO_VERSION=1.24
+
+FROM golang:${GO_VERSION}-bookworm AS build
+WORKDIR /src
+
+COPY go.mod ./
+RUN go mod download
+
+COPY . .
+
+ARG TARGETOS=linux
+ARG TARGETARCH=amd64
+RUN CGO_ENABLED=0 GOOS=${TARGETOS} GOARCH=${TARGETARCH} \
+    go build -trimpath -ldflags="-s -w" -o /out/authproxy ./cmd/authproxy
+
+FROM gcr.io/distroless/static-debian12:nonroot
+COPY --from=build /out/authproxy /authproxy
+
+EXPOSE 8080
+USER nonroot:nonroot
+
+ENTRYPOINT ["/authproxy"]