Add json and xml support to the post method in socket client

[simpleadm]

Added json and xml support to the post method in \Magento\Framework\HTTP\Client\Socket class

Description

In Pull Request #8373 was added ability to use json and xml in \Magento\Framework\HTTP\Client\Curl class, but in the class \Magento\Framework\HTTP\Client\Socket, which implements the same interface, that functionality wan't added. So current PR will fix it.

Related issue and PRs

• CURL Json POST CURL Json POST #3489

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)

[orlangur]

Hi @simpleadm, the changes looks good to me, however, we need to deliver them into 2.2-develop branch first in order to get this PR processed. Could you please prepare such a new pull request against 2.2-develop target branch.

[simpleadm]

Hi @orlangur , easy :)
For 2.2-develop #14347
For 2.1-develop #14348