Add commands for managing snippets in Azure Static Web Apps

**Related command**

`az staticwebapp`

**Is your feature request related to a problem? Please describe.**

Our CI/CD solution is able to spin up new ephemeral environments of our whole system, and also deprovision them when they are no longer needed. Such an environment includes dozens of Azure resources of different types, including an environment in a global static web app. The Azure CLI provides commands for managing environments, so we can automate that part — all good there.

However, each environment also needs a snippet, that tells our web app which backend API to connect to. This snippet needs to be unique per environment. Our automated provisioning and deprovisioning should ideally also include creating/deleting these snippets. However, currently, the only way to create and manage such snippets is manually through the portal, which makes automation impossible.

This is currently the only thing we are not able to automate.

**Describe the solution you'd like**

We would like 4 new commands added:

```
az staticwebapp snippet create
az staticwebapp snippet list
az staticwebapp snippet show
az staticwebapp snippet delete
```

**Describe alternatives you've considered**

There are no alternatives.