EZP-28774: Marked PAPI services as public

[adamwojs]

Question	Answer
JIRA issue	EZP-28774
Bug/Improvement	yes
New feature	no
Target version	master
BC breaks	no
Tests pass	yes
Doc needed	no

Since the Symfony 3.4, services which do not specify explicit their visibility are private by default (Ref. https://symfony.com/blog/new-in-symfony-3-4-services-are-private-by-default). Trying to access them directly from container (for instance using has or get method) will generate deprecation warning e.g. "User Deprecated: Checking for the initialization of the "ezpublish.api.repository" private service is deprecated since Symfony 3.4 and won't be supported anymore in Symfony 4.0." (Ref. https://github.com/symfony/symfony/blob/3.4/src/Symfony/Component/DependencyInjection/Container.php#L224)

This PR is a very first step to clean up logs from the deprecation warnings

TODO:

• Implement feature / fix a bug.
• Implement tests.
• Fix new code according to Coding Standards ($ composer fix-cs).
• Ask for Code Review.