Mark interfaces and blocks as API

[sivaschenko]

The following interfaces and blocks should be marked as API

AdobeImsApi/Api/LogInInterface.php
AdobeImsApi/Api/LogOutInterface.php
Magento\AdobeIms\Block\Adminhtml\SignIn

The fix should target future-develop branch

[gabrieldagama]

The fix should be targeted to develop branch instead.