🔖(minor) release 3.1.0

Added:
- 🚩(backend) add feature flag for the footer
- 🔧(backend) add view to manage footer json
- ✨(frontend) add custom css style
- 🚩(frontend) conditionally render AI button only
  when feature is enabled

Changed:
- 🚨(frontend) block button when creating doc

Fixed:
- 🐛(back) validate document content in serializer
- 🐛(frontend) fix selection click
  past end of content

src/mail/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mail_mjml",
-  "version": "3.0.0",
+  "version": "3.1.0",
   "description": "An util to generate html and text django's templates from mjml templates",
   "type": "module",
   "dependencies": {