az functionapp create is not idempotent

**Describe the bug**
The `az functionapp create` command is not idempotent, which breaks the guidelines. If there is a function app running from package, running `az functionapp create` removes the deployed package (or at least the mechanism that wires the deployed package to the app).

**To Reproduce**

1. Create functionapp with cli. `az functionapp create -g test --consumption-plan-location centralus -n testidempotent -s testidempotent`
2. Deploy to functionpp from package (Visual Studio publish, devops pipelines, cli, kudu, etc)
3. Verify functionapp is running.
4. Run create again `az functionapp create -g test --consumption-plan-location centralus -n testidempotent -s testidempotent`
5. Verify running functionapp was removed.

**Expected behavior**
CLI has clear idempotent guidelines. Running this command twice should not remove/delete a running functionapp deployment.

**Additional context**
My contextual scenario, which is a common goal of the industry, is an idempotent CI/CD deployment pipeline that deploys infra & software in a single pipeline (deploying software to a known, declarative environment that sets itself to known state as part of deploy). As such, the pipeline would run the `az functionapp create` command before deploying the new function app build. Because of this bug, there is a window of down time between when the `az functionapp create` command completes and when the function app is built, tested, and deployed (can be minutes, hours, days if the deployment fails).