Dockerfile: document ALPINE_VERSION build-arg

Dockerfile

@@ -1,6 +1,10 @@
 # syntax=docker/dockerfile:1
 
 ARG BASE_VARIANT=alpine
+
+# ALPINE_VERSION sets the version of the alpine base image to use, including for the golang image.
+# It must be a supported tag in the docker.io/library/alpine image repository
+# that's also available as alpine image variant for the Golang version used.
 ARG ALPINE_VERSION=3.21
 ARG BASE_DEBIAN_DISTRO=bookworm
 

dockerfiles/Dockerfile.authors

@@ -1,5 +1,7 @@
 # syntax=docker/dockerfile:1
 
+# ALPINE_VERSION sets the version of the alpine base image to use.
+# It must be a supported tag in the docker.io/library/alpine image repository.
 ARG ALPINE_VERSION=3.21
 
 FROM alpine:${ALPINE_VERSION} AS gen

dockerfiles/Dockerfile.dev

@@ -1,6 +1,10 @@
 # syntax=docker/dockerfile:1
 
 ARG GO_VERSION=1.24.5
+
+# ALPINE_VERSION sets the version of the alpine base image to use, including for the golang image.
+# It must be a supported tag in the docker.io/library/alpine image repository
+# that's also available as alpine image variant for the Golang version used.
 ARG ALPINE_VERSION=3.21
 
 # BUILDX_VERSION sets the version of buildx to install in the dev container.

dockerfiles/Dockerfile.lint

@@ -1,6 +1,10 @@
 # syntax=docker/dockerfile:1
 
 ARG GO_VERSION=1.24.5
+
+# ALPINE_VERSION sets the version of the alpine base image to use, including for the golang image.
+# It must be a supported tag in the docker.io/library/alpine image repository
+# that's also available as alpine image variant for the Golang version used.
 ARG ALPINE_VERSION=3.21
 ARG GOLANGCI_LINT_VERSION=v2.1.5
 

dockerfiles/Dockerfile.vendor

@@ -1,6 +1,10 @@
 # syntax=docker/dockerfile:1
 
 ARG GO_VERSION=1.24.5
+
+# ALPINE_VERSION sets the version of the alpine base image to use, including for the golang image.
+# It must be a supported tag in the docker.io/library/alpine image repository
+# that's also available as alpine image variant for the Golang version used.
 ARG ALPINE_VERSION=3.21
 ARG MODOUTDATED_VERSION=v0.8.0