chore: Miscellaneous cleanups and usability improvements

[wgrant]

what

Various cleanups and usability improvements made while iterating on #11:

• Allow hyphens in the prefix.
• Allow customising the resource group name.
• Provide a default resource group location.
• Allow Terraform to force-delete a non-empty resource group, since Application Insights creates other resources automatically.
• Allow configuration of the subscription ID without setting ARM_SUBSCRIPTION_ID.
• Create the app role assignment using an actual Terraform resource, not a subprocess call.
• Fix Application Insights plan noise.
• Fix DOS line endings.

Upgrades will need to terraform import azuread_app_role_assignment.stacklet_app_role_assignment /servicePrincipals/<SERVICE-PRINCIPAL-ID>/appRoleAssignedTo/<APP-ROLE-ASSIGNMENT-ID>. The service principal ID is the object_id field of azuread_service_principal.stacklet_sp[0], and you can find the role assignment ID with az rest --method GET --uri "https://graph.microsoft.com/v1.0/servicePrincipals/<SERVICE-PRINCIPAL-ID>/appRoleAssignedTo".

why

Iterating on changes was annoying. These changes were mostly originally from #11.

testing

On my test deployment.

[fwereade]

Thanks, this LGTM, but I'm weirded out by __init__.py showing up in the diff – what actually changed there?

[wgrant]

You should avert your eyes; it used... DOS line endings.