Fixes #12832

When logging in using a site address, we used to make a call to /sites/$site to fetch more info about the site and to determine if we should treat it as a WordPress.com site or a self-hosted one.

That endpoint did not work well with private sites, which would cause issues for users that had custom domains and 2FA enabled (you can read more about it in the linked issue or in this internal ref: pbArwn-16v-p2).

This PR replaces the usage of that endpoint with /connect/site-info, which allows us to better handle those situations. This endpoint was already being implemented in the LoginFlow library, but was only used by the Woo app. I tried to reuse some of that code, while also making sure to keep the existing behavior regarding how to treat different site types (WordPress.com, Jetpack and self-hosted).

To test

You can test the following scenarios by creating sites with jurassic.ninja or by using a pre-configured test site.

Main Scenario

Private WordPress.com site with custom domain and 2FA enabled

0. Clear app data.
1. On the Prologue screen, if the Smart Lock dialog appears, dismiss it.
2. Tap Enter your site address.
3. On the Site Address screen, enter a site address for a private WordPress.com site with a custom domain and 2FA enabled.
4. Tap Continue.
5. Notice the Username/Password screen.
6. Enter the username and password associated with the site.
7. Tap Continue.
8. Notice that the 2FA screen was displayed with no errors.
9. Enter the two-factor authentication code.
10. Tap Continue.
11. Complete the login flow normally.

Secondary Scenarios

WordPress.com, Self-Hosted or Jetpack site

0. Clear app data.
1. On the Prologue screen, if the Smart Lock dialog appears, dismiss it.
2. Tap Enter your site address.
3. On the Site Address screen, enter either a WordPress.com, a Self-Hosted or a Jetpack site address.
4. Tap Continue.
5. Notice the Username/Password screen.
6. Enter the username and password associated with the site.
7. Tap Continue.
8. Complete the login flow normally.

Note: While working on this PR, it was noted that Atomic and Jetpack sites are being treated as Self-Hosted sites as opposed to WP.com sites, which is the expected behavior. This will be addressed in a follow-up PR.

HTTP Auth

0. Clear app data.
1. On the Prologue screen, if the Smart Lock dialog appears, dismiss it.
2. Tap Enter your site address.
3. On the Site Address screen, enter http://do.wpmt.co/httpauth/.
4. Tap Continue.
5. Notice the Authorization Required dialog asking for the username/password pair for HTTP Basic Auth.

Self-Signed SSL

0. Clear app data.
1. On the Prologue screen, if the Smart Lock dialog appears, dismiss it.
2. Tap Enter your site address.
3. On the Site Address screen, enter https://do2.wpmt.co/vanilla/.
4. Tap Continue.
5. Notice the Invalid SSL Certificate dialog asking for a confirmation of the self-signed SSL certificate.

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.