FEATURE: Mixtral for summarization (#381)

lib/completions/endpoints/vllm.rb

@@ -11,7 +11,7 @@ module DiscourseAi
         end
 
         def default_options
-          { max_tokens_to_sample: 2000, model: model }
+          { max_tokens: 2000, model: model }
         end
 
         def provider_id

lib/summarization/entry_point.rb

@@ -18,6 +18,7 @@ module DiscourseAi
             max_tokens: SiteSetting.ai_hugging_face_token_limit,
           ),
           Models::Gemini.new("gemini-pro", max_tokens: 32_768),
+          Models::Mixtral.new("mistralai/Mixtral-8x7B-Instruct-v0.1", max_tokens: 32_000),
         ]
 
         foldable_models.each do |model|