feat: add config for mail server name (#13632)

fix #13627

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
* Added configurable display names for primary and fallback SMTP
servers, improving email sender identification.
* Defaults to “AFFiNE Server,” with support for MAILER_SERVERNAME
environment variable for the primary SMTP.
* Exposed in admin settings for easy setup alongside existing SMTP
options.
* Names are now passed through to mail transport options for consistent
use across emails.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/admin/src/config.json

@@ -89,6 +89,11 @@
     }
   },
   "mailer": {
+    "SMTP.name": {
+      "type": "String",
+      "desc": "Name of the email server (e.g. your domain name)",
+      "env": "MAILER_SERVERNAME"
+    },
     "SMTP.host": {
       "type": "String",
       "desc": "Host of the email server (e.g. smtp.gmail.com)",
@@ -123,6 +128,10 @@
       "type": "Array",
       "desc": "The emails from these domains are always sent using the fallback SMTP server."
     },
+    "fallbackSMTP.name": {
+      "type": "String",
+      "desc": "Name of the fallback email server (e.g. your domain name)"
+    },
     "fallbackSMTP.host": {
       "type": "String",
       "desc": "Host of the email server (e.g. smtp.gmail.com)"