Replace Jenkinsfile with GitHub Actions CI, release and lint tooling

Dockerfile

@@ -4,6 +4,7 @@ FROM --platform=$BUILDPLATFORM golang:1.27-alpine AS build
 
 ARG TARGETOS
 ARG TARGETARCH
+ARG TARGETVARIANT
 
 WORKDIR /build
 
@@ -11,7 +12,7 @@ COPY go.mod go.sum ./
 RUN go mod download
 
 COPY . .
-RUN CGO_ENABLED=0 GOOS=${TARGETOS} GOARCH=${TARGETARCH} \
+RUN CGO_ENABLED=0 GOOS=${TARGETOS} GOARCH=${TARGETARCH} GOARM=${TARGETVARIANT#v} \
     go build -trimpath -ldflags "-s -w" -o app ./cmd/app