introduce go.mod for env2yaml (#15921)

Update the env2yaml to have a go.mod instead of relying on disabling go modules, otherwise building with golang 1.22 will fail in the future.
This change also directly uses the golang image to build the binary removing the need for an intermediate image.

(cherry picked from commit 5c3e64d)

docker/Makefile

@@ -193,16 +193,12 @@ venv: requirements.txt
 	for i in 0 1 2 3 4 5; do sleep "$i"; pip install -r requirements.txt && break; done &&\
 	touch venv
 
-# Make a Golang container that can compile our env2yaml tool.
-golang:
-	docker build -t golang:env2yaml data/golang
-
 # Compile "env2yaml", the helper for configuring logstash.yml via environment
 # variables.
-env2yaml: golang
-	docker run --rm -i \
-	  -v $(PWD)/data/logstash/env2yaml:/usr/local/src/env2yaml:Z \
-	  golang:env2yaml
+env2yaml:
+	docker run --rm \
+	  -v "$(PWD)/data/logstash/env2yaml:/usr/src/env2yaml" \
+		-w /usr/src/env2yaml golang:1 go build
 
 # Generate the Dockerfiles from Jinja2 templates.
 dockerfile: venv templates/Dockerfile.j2

docker/data/logstash/env2yaml/go.mod

@@ -0,0 +1,5 @@
+module logstash/env2yaml
+
+go 1.21
+
+require gopkg.in/yaml.v2 v2.4.0

docker/data/logstash/env2yaml/go.sum

@@ -0,0 +1,3 @@
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=
+gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=