consider switching to azurerm, or at least adjust variable spec

[kewalaka]

with workload profile now supported, I'm keen to modify the module back to using azurerm again.

regardless, even if it is kept as azapi, I believe the variable block (module inputs) should be aligned to what azurerm looks like, as close as reasonable, and use snake_casing.

@segraef if you're in agreement I'd like to do this before we publish v0.1.0.

[segraef]

Since we're still at 0.1.0 fine with that, it would look differently if we'd have been at 1.0.0 already 😄