[RFE] Provide a mantle / kola flag to prefix azure resource groups with a custom string

[t-lo]

Current situation

kola creates Azure resource groups with the static prefix kola-cluster.

Impact

All kola created resource groups have the same prefix. This makes CI resources indistinguishable from nightlies and release builds, and from manual test runs.

Ideal future situation

Users can provide a custom prefix via a new --azure-resource-group-basename command line flag.

Implementation options

It seems advisable to not re-use the existing --basename flag for resource groups because this would impact existing use / automation of kola (e.g. cleanup jobs).