az lab create

**Is your feature request related to a problem? Please describe.**
There is no `az lab create` command.

**Describe the solution you'd like**
An `az lab create` command would allow us to create labs via cli. Nearly all other `az lab` commands exist.

**Describe alternatives you've considered**
You can deploy it with an ARM template or portal. Ideally, the cli can manage everything. We want to allow devs to spin up their own devtest labs. They're used to the cli. Telling them to do one thing with an arm template and everything else with the cli is a disjointed experience. Sure, you can deploy an ARM template with the cli, but it seems like it should fit the rest of the experience.