Wrong Doctrine DBAL storage connection is used when a new connection is appended in a 3rd party bundle.

Steps to reproduce

1. Install clean 3.1.1-EE.
2. Install and enable a custom bundle wich appends doctrine DBAL connection. Let's say `MyBundle` appends a new `myconnection` DBAL connection.
3. Try open Admin UI

Expected result

**Admin UI loads and the user is able to use it.

Actual result

**Database error is shown

It happens only on EE. Because no default connection is provided in https://github.com/ezsystems/ezplatform-ee/blob/master/config/packages/doctrine.yaml#L12-L30. And when 3rd party bundle appends a new connection, is it listed as the first connection, and it is used for storage:

$ php bin/console debug:container --parameter=doctrine.connections --format=json
{
    "doctrine.connections": {
        "myconnection": "doctrine.dbal.myconnection_connection",
        "default": "doctrine.dbal.default_connection",
        "site_factory": "doctrine.dbal.site_factory_connection"
    }
}