re-init the hosted agent project on new azd environment

The `init` step sets env vars using the agent.yaml and the users selections, but if you do `azd env new` then some env vars could be missing like AZURE_AI_PROJECT_ENDPOINT, AZURE_AI_PROJECT_ACR_CONNECTION_NAME, AZURE_CONTAINER_REGISTRY_ENDPOINT, APPLICATIONINSIGHTS_CONNECTION_NAME, AZURE_AI_PROJECT_ID, etc.

To repro, start a hosted agent and get it setup (no need to provision). Then do azd env new and try azd up.

I'd expect to go through the entire init flow again on a new environment.