Allow to set Azure location/region in extra specs

[pothos]

Since one can easily hit resource limits in a region it would be nice to have a way of spreading the pools over multiple regions. Currently one would need to define the provider multiple times.
It would be a nice improvement if one could set the location in the extra specs per pool. Having multiple pools requires labels to distinguish them - this label could be created automatically by deriving it from the location.

[gabriel-samfira]

This would require some changes to the GARM external provider API, which would send extra specs for all operations not just CreateInstance. Will do with the next GARM release.