TASK: WIP Prepare for synchronous content repository

[mhsdesign]

In preparation for #4988 this will adjust the cr to be synchronous already via a hack and adds a slim b/c block layer which will be removed with the next beta to ease migration.

Upgrade instructions

The CommandResult::block calls must be removed as the backwards compatibility layer will be removed with next beta.

- $contentRepository->handle($command)->block();
+ $contentRepository->handle($command);

Review instructions

Checklist

• Code follows the PSR-2 coding style
• Tests have been created, run and adjusted as needed
• The PR is created against the lowest maintained branch
• Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• Reviewer - The first section explains the change briefly for change-logs
• Reviewer - Breaking Changes are marked with !!! and have upgrade-instructions