expose imap username field (#15866)

Had an edge with a customer where they had a custom username.

packages/twenty-server/src/engine/core-modules/imap-smtp-caldav-connection/services/imap-smtp-caldav-connection.service.ts

@@ -31,7 +31,7 @@ export class ImapSmtpCaldavService {
       port: params.port,
       secure: params.secure ?? true,
       auth: {
-        user: handle,
+        user: params.username ?? handle,
         pass: params.password,
       },
       logger: false,