New rule: Ensure link are at the bottom of the file

[alamirault]

Fix #1512

FYI when I run it on Symfony docs I have "only" 2 errors 😄

frontend/encore/faq.rst ✘
  140: Please move link line at the bottom of the file
   ->  .. _`rsync`: https://rsync.samba.org/
  171: Please move link line at the bottom of the file
   ->  .. _`Webpack integration in PhpStorm`: https://www.jetbrains.com/help/phpstorm/using-webpack.html

contributing/code/conventions.rst ✘
  184: Please move link line at the bottom of the file
   ->  .. _`ServiceRouterLoader`: https://github.com/symfony/symfony/blob/4.4/src/Symfony/Component/Routing/Loader/DependencyInjection/ServiceRouterLoader.php

[OskarStark]

Great 👌🏻🤓

But I spotted another idea for a new rule:

.. _ServiceRouterLoader: https://github.com/symfony/symfony/blob/4.4/src/Symfony/Component/Routing/Loader/DependencyInjection/ServiceRouterLoader.php

This links to 4.4 and should link to 5.4

[OskarStark]

"Please move link definition to the bottom of the page" as error message

[alamirault]

Great 👌🏻🤓

But I spotted another idea for a new rule:

.. _ServiceRouterLoader: https://github.com/symfony/symfony/blob/4.4/src/Symfony/Component/Routing/Loader/DependencyInjection/ServiceRouterLoader.php

This links to 4.4 and should link to 5.4

It can be replaced by {version}. (I will check missing occurences in docs)
Not sure this rule is required now as we don't have this problem on new contributions I think