Configuration label and tooltip cleanup

[layoutd]

Changes proposed in this Pull Request:

This PR revises some fields labels related to Facebook Sync, adds a few tooltips, and adds links to more information at the bottom of Advertise, Product sync, and in the Debug section options.

Pending is adding a documentation link at the bottom of Product Sets, but would probably need some DOM element manipulation with JS, so leaving that one for a different PR.

It also clears up some Product Editor form issues where the Custom Image URL field was always displayed initially, and makes the field contingent on the "Use custom image" option being selected.

• [x] Do the changed files pass phpcs checks? Please remove phpcs:ignore comments in changed files and fix any issues, or delete if not practical.

Screenshots:

Detailed test instructions:

1. Check that all learn more links work correctly.
2. Check text of learn more links and tooltips.
3. Confirm that the Custom Image URL field works correctly (displays and hides, saves, etc) on Simple and Variable products.

Changelog entry

Tweak - Tooltips, config labels, documentation links.

[message-dimke]

All the labels open proper documentation sections. Custom Image URL behaves correctly for Simple and Variable products when not in Block Product Editor.

Looks good! Thank you, @layoutd !

[layoutd]

Thanks @message-dimke!

I forgot to mention that I centered the Disconnect link vertically, very trivial but I think it's much better

Before

After