Make AccountFilter field and parameter names configurable

[javihgil]

Problem

AccountFilter is still hard-coded to account_id and _account.

Current code:

• src/Doctrine/Filter/AccountFilter.php:17 returns $targetTableAlias.'.account_id = '.$this->getParameter('_account')

Impact

The filter is not reusable enough for real applications:

• it assumes a fixed join column name
• it assumes a fixed Doctrine filter parameter name
• it is fragile when an application uses a different field name or mapping strategy

Expected behavior

• make the account field / association name configurable
• make the Doctrine parameter name configurable
• keep a sensible default for current integrations
• add tests for at least one non-default field or parameter configuration