iwa caching: trigger IWA updates manually after the installation

In ephemeral sessions `IsolatedWebAppUpdateManager` checks for updates
too early, even before IWAs are installed from cache. Which means
the IWA update will not be done even when the update is available.

This CL triggers the update check manually after the IWA installation
to avoid waiting for the next scheduled update check (which is
currently 5 hours).

Browser Tests: IwaCache*

Cache commands diagram: go/iwa-bundle-cache-operations

Fixed: 388727598
Change-Id: I98dae2e4a2ceb5a1a92d7e745f515941f2332bcb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6542653
Reviewed-by: Sergii Bykov <sbykov@google.com>
Commit-Queue: Irina Fedorova <irfedorova@google.com>
Reviewed-by: Andrew Rayskiy <greengrape@google.com>
Cr-Commit-Position: refs/heads/main@{#1460629}