feat: Introduce the concept of tool registry within Captain (#11516)

This PR introduces the concept of a tool registry. The implementation is
straightforward: you can define a tool by creating a class with a
function name. The function name gets registered in the registry and can
be referenced during LLM calls. When the LLM invokes a tool using the
registered name, the registry locates and executes the appropriate tool.
If the LLM calls an unregistered tool, the registry returns an error
indicating that the tool is not defined.

enterprise/app/services/captain/copilot/chat_service.rb

@@ -10,6 +10,8 @@ class Captain::Copilot::ChatService < Llm::BaseOpenAiService
     @conversation_history = config[:conversation_history]
     @previous_messages = config[:previous_messages] || []
     @language = config[:language] || 'english'
+
+    register_tools
     @messages = [system_message, conversation_history_context] + @previous_messages
     @response = ''
   end
@@ -25,6 +27,11 @@ class Captain::Copilot::ChatService < Llm::BaseOpenAiService
 
   private
 
+  def register_tools
+    @tool_registry = Captain::ToolRegistryService.new(@assistant)
+    @tool_registry.register_tool(Captain::Tools::SearchDocumentationService)
+  end
+
   def system_message
     {
       role: 'system',