Chain the flow of allowlist checking and walletable pass extraction

This CL connects the flow for detecting walletable passes on a web page,
from checking the allowlist to invoking the extraction model.

A new public method, `StartWalletablePassDetectionFlow`, is introduced
in the base `WalletablePassIngestionController`. This flow is triggered
from `DidFinishLoad` and performs the following steps in sequence:

1. Checks if the page's URL is on the Optimization Guide allowlist for
pass detection.

2. If the page is eligible, it fetches the annotated page content.

3. Once the content is available, it calls ExtractWalletablePass to
trigger the server-side model execution.

Bug: 442454641
Change-Id: I0ae053f0e5e63104e3c3fafccd1ddcbcdc310f61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6906557
Reviewed-by: Bruno Braga <brunobraga@google.com>
Commit-Queue: Hanfeng Zhu <hanfeng@google.com>
Reviewed-by: Norge Vizcay <vizcay@google.com>
Cr-Commit-Position: refs/heads/main@{#1512891}