feat: email templates

adds email templates using `react-email` which will be used for invites,
signing and document completion.

authored by @dephraiim

packages/email/tailwind.config.js

@@ -0,0 +1,11 @@
+/* eslint-disable @typescript-eslint/no-var-requires */
+const baseConfig = require('@documenso/tailwind-config');
+const path = require('path');
+
+module.exports = {
+  ...baseConfig,
+  content: [
+    `templates/**/*.{ts,tsx}`,
+    `${path.join(require.resolve('@documenso/ui'), '..')}/**/*.{ts,tsx}`,
+  ],
+};