GitHub Action to Generate OpenAPI Document within CI/CD Pipeline

[justinyoo]

Describe the issue

We need a GitHub Action to generate the OpenAPI document on-the-fly after building an Azure Functions app within a CI/CD pipeline.

Additional context

Related to #366

There are many requests for a CLI to auto-generate the OpenAPI document, which is mainly for the CI/CD pipeline use. But it's technically possible for those auto-generation within this context.

Similar approach has already been applied to this repo's GitHub Actions workflow:

https://github.com/Azure/azure-functions-openapi-extension/blob/e432a6bcdcd6f060f8a0cc58db680066f20157cb/.github/workflows/main-build.yaml#L77-L108