Update Apache server configuration for Flex

[weaverryan]

See #8693. Basically, Symfony 4 won't ship with a .htaccess file anymore. But see symfony/recipes#190 (comment) - we may have a recipe for it soon. So, this is kind of blocked until we figure that out.

[xabbuh]

Now that we have a pack, should we do anything here?

[weaverryan]

We need to wait for the recipe to be created, then we can document that you need to install it for Apache (or put the rewrite rules into your vhost if you prefer)

The recipe has been created by @fabpot in symfony/apache-pack. However, this recipe is empty.

As for the article in the documentation; I think we can add this as an x within setup/flex.rst:

Using Flex With The Apache Webserver
------------------------------------

Or we make a new node at setup/web_server_configuration.rst about configure Apache for Flex by using the recipe.

@fabpot: What is the status of the symfony/apache-pack?
@weaverryan: In what doc page are we going to put this?

[fabpot]

See symfony/recipes#190