Added condition to include client code in the search when the global variable SOCIETE_ADD_REF_IN_LIST is set to 1.

- Modified the SQL query to include 's.code_client' in the search conditions.
- Added check for the global variable SOCIETE_ADD_REF_IN_LIST.
- If SOCIETE_ADD_REF_IN_LIST is 1, 's.code_client' is included in the search along with 's.nom' and 's.name_alias'.
- Ensured that 's.code_client' is searched separately only when SOCIETE_ADD_REF_IN_LIST is 1 and 'search_societe' is not defined.

Refactor: Replace conf->global->SOCIETE_ADD_REF_IN_LIST with getDolGlobalString('SOCIETE_ADD_REF_IN_LIST')

Simplified SOCIETE_ADD_REF_IN_LIST retrieval

Replaced conditional retrieval with getDolGlobalInt('SOCIETE_ADD_REF_IN_LIST') to simplify code and pass tests.