MM-21769 - Validate plugin bundle and signature files when pac… (#13629)

* MM-21769 - Validate plugin bundle and signature files when packaging MM

* Renamed public key, using gpg exit code to verify success

* Update Makefile

Co-Authored-By: Jesse Hallam <jesse.hallam@gmail.com>

* Pulling platform specific prepackaged plugins

* Verify platform specific plugin binary exist when building each ARCH

Co-authored-by: Jesse Hallam <jesse.hallam@gmail.com>

Makefile

@@ -1,4 +1,4 @@
-.PHONY: build package run stop run-client run-server stop-client stop-server restart restart-server restart-client start-docker clean-dist clean nuke check-style check-client-style check-server-style check-unit-tests test dist prepare-enteprise run-client-tests setup-run-client-tests cleanup-run-client-tests test-client build-linux build-osx build-windows internal-test-web-client vet run-server-for-web-client-tests diff-config
+.PHONY: build package run stop run-client run-server stop-client stop-server restart restart-server restart-client start-docker clean-dist clean nuke check-style check-client-style check-server-style check-unit-tests test dist prepare-enteprise run-client-tests setup-run-client-tests cleanup-run-client-tests test-client build-linux build-osx build-windows internal-test-web-client vet run-server-for-web-client-tests diff-config prepackaged-plugins
 
 ROOT := $(dir $(abspath $(lastword $(MAKEFILE_LIST))))
 
@@ -151,6 +151,14 @@ endif
 plugin-checker:
 	$(GO) run $(GOFLAGS) ./plugin/checker
 
+prepackaged-plugins: ## Populate the prepackaged-plugins directory
+	@echo Downloading prepackaged plugins
+	mkdir -p prepackaged_plugins
+	@cd prepackaged_plugins && for plugin_package in $(PLUGIN_PACKAGES) ; do \
+		curl -f -O -L https://plugins-store.test.mattermost.com/release/$$plugin_package.tar.gz; \
+		curl -f -O -L https://plugins-store.test.mattermost.com/release/$$plugin_package.tar.gz.sig; \
+	done
+
 golangci-lint: ## Run golangci-lint on codebase
 # https://stackoverflow.com/a/677212/1027058 (check if a command exists or not)
 	@if ! [ -x "$$(command -v golangci-lint)" ]; then \