E2E tests: relax CS assertion for v3

What does this MR do and why?

Resolves https://gitlab.com/gitlab-org/gitlab/-/issues/498373

Handles response for v3 of code suggestions endpoint, so we can enable #477891 (closed)

/v3/code/completions changes the response structure in the following way (no id, new metadata object for example):

--- a/qa/qa/specs/features/ee/api/3_create/code_suggestions_spec.rb
+++ b/qa/qa/specs/features/ee/api/3_create/code_suggestions_spec.rb
@@ -10,15 +10,13 @@ module QA
     describe 'Code Suggestions' do
       let(:expected_response_data) do
         {
-          id: 'id',
+          metadata: {
           model: {
             engine: anything,
             name: anything,
-            lang: 'ruby',
-            tokens_consumption_metadata: anything
-          },
-          object: 'text_completion',
-          created: anything
+            lang: 'ruby'
+          }, timestamp: anything },
           choices: anything
         }
       end

To handle both V2 and V3 we will relax the assertion to check only for choices until the anthropic_code_gen_aigw_migration is completely rolled out.

Test passing in this MR: https://gitlab.com/gitlab-org/gitlab/-/jobs/8057513605

Test passing in staging with anthropic_code_gen_aigw_migration FF turned on: https://ops.gitlab.net/gitlab-org/quality/staging/-/jobs/15658225

Test passing in staging without anthropic_code_gen_aigw_migration FF turned on: https://ops.gitlab.net/gitlab-org/quality/staging/-/jobs/15657322

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