Add `make archive` for uploading source code tarball

* git default source code tarballs have a tendency of changing shasums

Makefile

@@ -292,16 +292,20 @@ bundle-darwin: binary-darwin
 .PHONY: binary-linux binary-darwin bundle-linux bundle-darwin
 
 #################################################
-# Targets for creating OS specific artifacts
+# Targets for creating OS specific artifacts and archives
 #################################################
 
 artifacts-linux-tag: bundle-linux debian
 
 artifacts-darwin-tag: bundle-darwin
 
+artifacts-archive-tag:
+	$Q mkdir -p $(RELEASE)
+	$Q git archive v$(VERSION) | gzip > $(RELEASE)/step-certificates.tar.gz
+
 artifacts-tag: artifacts-linux-tag artifacts-darwin-tag
 
-.PHONY: artifacts-linux-tag artifacts-darwin-tag artifacts-tag
+.PHONY: artifacts-linux-tag artifacts-darwin-tag artifacts-archive-tag artifacts-tag
 
 #################################################
 # Targets for creating step artifacts
@@ -310,6 +314,9 @@ artifacts-tag: artifacts-linux-tag artifacts-darwin-tag
 # For all builds that are not tagged
 artifacts-master:
 
+# For all builds with a release-candidate (-rc) tag
+artifacts-release-candidate: artifacts-tag
+
 # For all builds with a release tag
 artifacts-release: artifacts-tag