Exclude LYS coming soon page for WPCOM share link

[chihsuan]

Changes proposed in this Pull Request:

Closes https://github.com/Automattic/wc-calypso-bridge/issues/1499.

Add a filter to exclude LYS coming soon page for WPCOM share link

• When LYS private link is turned on, LYS private link should bypass coming soon mode.
• When WPCOM private link is turned on, WPCOM private link should bypass coming soon mode.

• [ ] This PR is a very minor change/addition and does not require testing instructions (if checked you can ignore/remove the next section).

How to test the changes in this Pull Request:

• [ ] Have you followed the Writing high-quality testing instructions guide?

1. Use a WPCOM atomic e-commerce site
2. Enable LYS feature flag
3. Go to https://wordpress.com/settings/general/SITE_URL and enable WPCOM coming soon
4. Go to /wp-admin/admin.php?page=wc-settings&tab=site-visibility and enable LYS coming soon
5. Open the site frontend in an incognito window and confirm that the LYS coming soon page is shown
6. Enable WPCOM share link and use the share link to open the site in an incognito window
7. Confirm that the LYS coming soon page is not shown
8. Confirm that you can use LYS private link to bypass coming soon mode

Other information:

• [x] Have you added an explanation of what your changes do and why you'd like us to include them?
• [ ] Have you written new tests for your changes, as applicable?

FOR PR REVIEWER ONLY:

• [ ] I have reviewed that everything is sanitized/escaped appropriately for any SQL or XSS injection possibilities. I made sure Linting is not ignored or disabled.