Updating/work-with this template for Azd Devcontainer feature.

> Please provide us with the following information:
> ---------------------------------------------------------------

### This issue is for a: (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [x] feature request
- [ ] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
```

We are updating this template to support new features in `Azd Devcontainer`.

For the Azd Devcontainer feature: We will add the following code in `devcontainer.json` file.

```
"ghcr.io/azure/azure-dev/azd:latest": {}
```
And remove the relevant code for installing `azd` in `Dockerfile` under `.devcontainer` folder.
```
RUN curl -fsSL https://aka.ms/install-azd.sh | bash \
```

@rajeshkamal5050 , @paulyuk , @greenie-msft for notification.