feat: implement rolling builds (#910)

This diff modifies all the github actions that produce assets to
publish on a release called rolling when we are not building a tag.

If everything goes as planned, we should be able to provide
people with automatically generated fresh binaries for testing.

While there, introduce caching for all builds to make them
as fast as possible. I suspect gomobile based builds will not
see any speed up but other builds most likely will.

See https://github.com/ooni/probe/issues/2249

script/ghpublish.bash

@@ -0,0 +1,25 @@
+#!/bin/bash
+set -euo pipefail
+
+# 1. obtain the github ref of this action run
+__ref=${GITHUB_REF:-}
+
+if [[ $__ref == "" ]]; then
+	echo "FATAL: missing github ref" 1>&2
+	exit 1
+fi
+
+# 2. determine whether to publish to a release or to rolling
+if [[ $__ref =~ ^refs/tags/v ]]; then
+	__tag=${__ref#refs/tags/}
+else
+	__tag=rolling
+fi
+
+set -x
+
+# 3. create the release as a pre-release unless it already exists
+gh release create -p $__tag --target $GITHUB_SHA || true
+
+# 4. publish all the assets passed as arguments to the target release
+gh release upload $__tag --clobber "$@"

script/maketarball.bash

@@ -0,0 +1,28 @@
+#!/bin/bash
+
+set -euo pipefail
+
+# 1. obtain the github ref of this action run
+__ref=${GITHUB_REF:-}
+
+if [[ $__ref == "" ]]; then
+	echo "FATAL: missing github ref" 1>&2
+	exit 1
+fi
+
+# 2. determine whether to publish to a release or to rolling
+if [[ $__ref =~ ^refs/tags/v ]]; then
+	__version=${__ref#refs/tags/v}
+else
+	__version=rolling
+fi
+
+set -x
+
+# 3. make sure we're using the correct go version
+./CLI/check-go-version
+
+# 4. generate the actual tarball
+go mod vendor
+tar -czf ooni-probe-cli-${__version}.tar.gz --transform "s,^,ooni-probe-cli-${__version}/," *
+