[Refactor] Relocate tests from tests/v1/entrypoints/ to tests/entrypoints/

[sfeng33]

Purpose

Consolidate tests so that all entrypoint tests are centralized in the same folder:

• Move test_struct_output_generate.py to tests/entrypoints/llm/
• Move test_chat_completion.py, test_completion_with_image_embeds.py to
  tests/entrypoints/openai/chat_completion/
• Move test_completion.py to tests/entrypoints/openai/completion/
• Move test_multi_api_servers.py to tests/entrypoints/openai/
• Delete tests/v1/entrypoints/

CI changes

• Update all path references in .buildkite/ configs, CODEOWNERS, and mergify.yml
• Remove dedicated "V1 Test entrypoints" jobs from AMD CI (tests are now covered by existing entrypoints jobs)
• Add --ignore=entrypoints/openai/test_multi_api_servers.py to broad entrypoints/openai sweeps in entrypoints.yaml and test-amd.yaml to prevent double-running (it's already run explicitly with DP_SIZE=2 in distributed CI)

[gemini-code-assist]

Code Review

This pull request effectively relocates test files from tests/v1/entrypoints/ to tests/entrypoints/ and updates all corresponding path references in .buildkite configurations, CODEOWNERS, and mergify.yml. The changes also correctly remove dedicated "V1 Test entrypoints" jobs from CI, ensuring that tests are now covered by existing entrypoints jobs and preventing double-running of test_multi_api_servers.py. The consolidation of test files and associated configuration updates are well-executed and align with the stated purpose of centralizing entrypoint tests, improving the overall organization and maintainability of the test suite.

[DarkLight1337]

This makes sense but would like @robertgshaw2-redhat to take a look, as I'm not 100% sure what was the original intention of V1 entrypoints tests

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @sfeng33.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[sfeng33]

Rebase to merge conflict