Added RewriteBase directive template in .htaccess file into pub/media folder

[ccasciotti]

Description

This PR adds RewriteBase directive template into .htaccess file under pub/media folder, useful in case the need is to install Magento code under a directory inside the web root.
Setting this directive into .htaccess file in Magento's root and without setting it into .htaccess under pub/media folder cause a media file missing by Apache Web Server due to specified RewriteRule directive that points to ../get.php.
A similar issue was already fixed in #13678 and relative branch portings.

Fixed Issues

none

Manual testing scenarios

none

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)

[magento-engcom-team]

Hi @ccasciotti. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me 2.3-develop instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[magento-engcom-team]

Hi @dmytro-ch, thank you for the review.
ENGCOM-4167 has been created to process this Pull Request

[ghost]

Hi @ccasciotti, thank you for your contribution!
Please, complete Contribution Survey, it will take less than a minute.
Your feedback will help us to improve contribution process.