build: consolidate Dockerfiles for multi-architecture support

- Add a new Dockerfile for multi-architecture support using Alpine 3.20
- Remove Dockerfile for linux.amd64
- Remove Dockerfile for linux.arm
- Remove Dockerfile for linux.arm64
- Remove Dockerfile for windows
- Remove Docker manifest template file

Signed-off-by: appleboy <appleboy.tw@gmail.com>

docker/Dockerfile

@@ -0,0 +1,20 @@
+FROM alpine:3.20
+
+ARG TARGETOS
+ARG TARGETARCH
+
+LABEL maintainer="Bo-Yi Wu <appleboy.tw@gmail.com>" \
+  org.label-schema.name="Drone Jenkins Plugin" \
+  org.label-schema.vendor="Bo-Yi Wu" \
+  org.label-schema.schema-version="1.0"
+
+LABEL org.opencontainers.image.source=https://github.com/appleboy/drone-jenkins
+LABEL org.opencontainers.image.description="Drone Jenkins"
+LABEL org.opencontainers.image.licenses=MIT
+
+RUN apk add --no-cache ca-certificates && \
+  rm -rf /var/cache/apk/*
+
+COPY release/${TARGETOS}/${TARGETARCH}/drone-jenkins /bin/
+
+ENTRYPOINT ["/bin/drone-jenkins"]