[package] allow to choose when build/packaging step occurs in the lifecycle

[sinedied]

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Output from azd version

azd version
azd version 1.4.1 (commit 1cbed85cf47ed235b5ed31868eda79619525bfcc)

Describe the issue
In microservices architectures where the frontend is deployed as a separate component, you need to get the backend/API location after the provisioning as the backend URL need to be provided at build time for static web apps.

We have the case for example in https://github.com/Azure-Samples/contoso-real-estate and https://github.com/Azure-Samples/azure-search-openai-javascript.

In the first sample, azd up cannot be used because of this, and it needs to run azd provision then azd deploy as a workaround.

In the second sample, we used a different workaround so that azd up could be used: we added a "predeploy" script to build the app just before deployment, but that effectively cause the app to be built twice.

This is a very common use case and it feels hacky to have to make twists like these to make it work.

Would it be possible to consider a step property under a build or package settings to define when the command should be ran? For example:

services:
  webapp:
    project: ./packages/webapp
    dist: dist
    language: ts
    host: staticwebapp
    package:
      step: predeploy

[pamelafox]

We would like this for the Python OpenAI sample as well.

[savannahostrowski]

@ellismg We talked about this briefly this morning but I could imagine a world where azure.yaml allows you to specify what happens in azd up

[savannahostrowski]

@rajeshkamal5050 based on the convo we had about extensibility a couple weeks ago, I've moved this to January.

[wbreza]

POC in development #3173