Support pipeline job context in Duo Chat

What does this MR do and why?

Allow Duo Chat users to ask questions about pipeline jobs.

AI Gateway MR: gitlab-org/modelops/applied-ml/code-suggestions/ai-assist!1379 (merged)

Evaluation results

Results for the master branch: master evaluation.

Results for this branch: MR evaluation.

Metric	Master branch	This branch
Correctness	3.64	3.62
Readability	3.66	3.67
Comprehensiveness	3.58	3.57

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

1. From Rails console enable feature flags:

Feature.enable(:ai_build_reader_for_chat)
Feature.enable(:v2_chat_agent_integration)

2. Run GDK.
3. In AI gateway repo checkout the 468461-support-pipeline-context-in-duo-chat branch and run AI gateway.
4. Visit a pipeline job and ask a question to Duo Chat about the pipeline (What is this pipeline about?)
5. You should receive a details about the build.

Related to #468461 (closed)

ee/spec/lib/gitlab/llm/chain/tools/build_reader/executor_spec.rb

@@ -224,6 +224,25 @@
             expect(tool.execute.content).to eq(response)
           end
         end
+
+        context 'with valid build url' do
+          let(:resource_id) { build1.id }
+          let(:ai_response) { "url\", \"ResourceIdentifier\": \"#{url}\"}" }
+          let(:url) { "https://example.com/some/path/-/builds/#{build1.id}" }
+
+          it_behaves_like 'success response'
+        end
+
+        context 'with invalid build url' do
+          let(:ai_response) { "url\", \"ResourceIdentifier\": \"#{url}\"}" }
+          let(:url) { "https://example.com/some/path/-/builds/1fd11" }
+
+          it "returns success response with an explanatory message" do
+            allow(tool).to receive(:request).and_return(ai_response)
+
+            expect(tool.execute.content).to eq("I'm sorry, I can't generate a response. Please try again.")
+          end
+        end
       end
     end
   end