[Functions] Add a flag to create the storage account in az functionapp create

**Is your feature request related to a problem? Please describe.**
No

**Describe the solution you'd like**
Add a flag to create the storage account in az functionapp create, this will not change the current behavior, also it will allow for a more streamlined approach to creating function apps

Intended behavior after this proposal:

1. If storage account information is provided --> use this [existing behavior]
2. If # 1 is not provided and create storage flag is provided --> create a storage account with appname-strg (need to make sure the name is valid) [new behavior]
3. If none are provided --> throw and error [existing behavior]
4. If # 1 and # 2 are provided, use the provided storage account