Aggiungere LLM Providers (#48)

* Refactor configs dei modelli
* Aggiunti Providers

.env.example

@@ -5,7 +5,14 @@
 # https://makersuite.google.com/app/apikey
 GOOGLE_API_KEY=
 
-
+# https://platform.openai.com/settings/organization/api-keys
+OPENAI_API_KEY=
+# https://admin.mistral.ai/organization/api-keys
+MISTRAL_API_KEY=
+# https://platform.deepseek.com/api_keys
+DEEPSEEK_API_KEY=
+# https://console.x.ai/team/%TEAM_ID%/api-keys
+XAI_API_KEY=
 ###############################################################################
 # Configurazioni per gli agenti di mercato
 ###############################################################################