Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/templates/Makefile

@@ -0,0 +1,19 @@
+# Directory containing mjml templates
+OUTPUT_DIR=.
+MJML=mjml
+
+## Also update the circleCI file if you update this.
+check-prereq: ## check if mjml is installed
+	@if ! [ -x "$$(command -v mjml)" ]; then \
+		echo "mjml is not installed. Installing mjml"; \
+		npm install -g mjml@4.9.0; \
+	fi;
+
+
+build: check-prereq ## Compile all mjml email templates
+	@for f in $(shell ls *.mjml); \
+	do \
+	  echo "{{define \"$${f%.*}\"}}\n" > $(OUTPUT_DIR)/$${f%.*}.html; \
+		$(MJML) $${f} -s >> $(OUTPUT_DIR)/$${f%.*}.html; \
+		echo "\n{{end}}" >> $(OUTPUT_DIR)/$${f%.*}.html; \
+	done