FEATURE: Allow sending group SMTP emails with from alias (#15687)

This commit allows group SMTP emails to be sent with a
different from email address that has been set up as an
alias in the email provider. Emails from the alias will
be grouped correctly using Message-IDs in the mail client,
and replies to the alias go into the correct group inbox.

spec/requests/api/schemas/json/group_response.json

@@ -221,6 +221,12 @@
             "null"
           ]
         },
+        "email_from_alias": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "email_password": {
           "type": [
             "string",