fix: rename email template placeholder from username to recipientName

Author: dkrizan

backend/data/src/test/kotlin/io/tolgee/email/EmailServiceTest.kt

@@ -216,7 +216,7 @@ class EmailServiceTest {
       "registration-confirm",
       Locale.ENGLISH,
       mapOf(
-        "username" to "bob@example.com",
+        "recipientName" to "bob@example.com",
         "confirmUrl" to "https://app.tolgee.io/verify/123/abc",
         "isSignup" to true,
       ),

email/emails/registration-confirm.tsx

@@ -36,8 +36,8 @@ export default function RegistrationConfirmEmail() {
       <Text style={{ margin: '0 0 16px' }}>
         <LocalizedText
           keyName="email-greetings"
-          defaultValue="Hello {username},"
-          demoParams={{ username: 'Bob' }}
+          defaultValue="Hello {recipientName},"
+          demoParams={{ recipientName: 'Bob' }}
         />
       </Text>
       <Text>