Move v1 to v1.6 

feat: support using the action with Azure-hosted OpenAI models (#47) This PR introduces a new, optional input to the GitHub Action, `responses-api-endpoint`, which makes it possible to use this Action with Azure. As explained in the updated `README.md`, if `responses-api-endpoint` is specified, it will be the URL that Codex hits to make Responses API requests. In practice, we expect this to be used mostly by Azure users. With the Azure account I just created, I got this working with the following configuration: ```yaml jobs: codex: runs-on: ubuntu-latest steps: - uses: actions/checkout@v5 - name: Start Codex proxy uses: 71690bb with: openai-api-key: ${{ secrets.AZURE_OPENAI_API_KEY }} responses-api-endpoint: "https://bolinfest-7804-resource.cognitiveservices.azure.com/openai/v1/responses" ``` Under the hood, if `responses-api-endpoint` is non-empty, it simply becomes the `--upstream-url` argument to `codex-responses-api-proxy`. TO DISCUSS: Better/shorter name than `responses-api-endpoint`? This PR builds on the work of openai/codex#6129.

@main -> @v1 (#25)