[iOS] Add TODO for security domain path in IOSTrustedVaultClient

Need to set the right security domain path in IOSTrustedVaultClient,
when calling TrustedVaultClientBackend APIs.

Bug: 343007092
Change-Id: I018cd9dabcd52486da2c3a49ca51e02eb650a958
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5722710
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Auto-Submit: Jérôme Lebel <jlebel@chromium.org>
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1329766}