[Port 2.3-develop] Show redirect_to_base config in store scope

[JeroenVanLeusden]

Description

Add web/unsecure/base_url config to website and store scope. Setting is used that way in the code, see:
https://github.com/magento/magento2/blob/2.3-develop/app/code/Magento/Store/App/FrontController/Plugin/RequestPreprocessor.php#L80-L83
https://github.com/magento/magento2/blob/2.3-develop/app/code/Magento/Store/Model/BaseUrlChecker.php#L50-L53

The tests also use store scope.

Fixed Issues (if relevant)

1. None I could find.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[JeroenVanLeusden]

@dmanners Backport of #13614, can you process this also?