feat: allows loginWithUsername to not require username (#7480)

Allows username to be optional when using the new loginWithUsername
feature. This can be done by the following:

```ts
auth: {
  loginWithUsername: {
    requireUsername: false, // <-- new property, default true
    requireEmail: false, // default: false
    allowEmailLogin: true, // default false
  },
},
```

test/auth/AuthDebug.tsx

@@ -15,7 +15,9 @@ export const AuthDebug: React.FC<UIField> = () => {
       setState(userRes)
     }
 
-    void fetchUser()
+    if (user?.id) {
+      void fetchUser()
+    }
   }, [user])
 
   return (

test/auth/e2e.spec.ts

@@ -56,7 +56,6 @@ const createFirstUser = async ({
   // forget to fill out confirm password
   await page.locator('#field-email').fill(devUser.email)
   await page.locator('#field-password').fill(devUser.password)
-  await wait(500)
   await page.locator('.form-submit > button').click()
   await expect(page.locator('.field-type.confirm-password .field-error')).toHaveText(
     'This field is required.',
@@ -66,7 +65,6 @@ const createFirstUser = async ({
   await page.locator('#field-email').fill(devUser.email)
   await page.locator('#field-password').fill('12')
   await page.locator('#field-confirm-password').fill('12')
-  await wait(500)
   await page.locator('.form-submit > button').click()
   await expect(page.locator('.field-type.password .field-error')).toHaveText(
     'This value must be longer than the minimum length of 3 characters.',
@@ -76,7 +74,6 @@ const createFirstUser = async ({
   await page.locator('#field-password').fill(devUser.password)
   await page.locator('#field-confirm-password').fill(devUser.password)
   await page.locator('#field-custom').fill('Hello, world!')
-  await wait(500)
   await page.locator('.form-submit > button').click()
 
   await expect