[MM-37726] - Self-managed: Update email template to new branding - Invitation email (#18200)

* [MM-37726] -  Self-managed: Update email template to new branding - Invitation email

* fix subtitle color

* fix other template subtitle colors

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

templates/partials/style.mjml

@@ -30,7 +30,7 @@
   .subTitle div {
     font-size: 16px !important;
     line-height: 24px !important;
-    color: rgb(63, 67, 80) !important;
+    color: rgba(63, 67, 80, 0.64) !important;
   }
 
   .subTitle a {