Werk #15753: agent_azure: Make resource group filter case-insensitive

Due to the inconsistant behaviour of the Azure API, the filtering of resources by resource group wasn't working as expected. The resource group name returned by the API was sometimes of a different case then the one visible in the Azure portal, which led to resources not being discovered by Checkmk.

Now, the resource group filtering is case-insensitive and the problem no longer occurrs.

To the list of all Werks