Implement support for account-switch-key

[jhoekstra]

Hi,

Since the default API-credentials can now be used for purging as well(as opposed to before with separate API-credential), would it be possible to add the possibility to use account-switch-keys for purging as well?
As a partner we manage multiple customers and to be able to purge with CLI is a timesaver, however still having to maintain separate credentials per customers for just purging is a bit of a pain.

An option to alias account-switch-keys would be welcomed as well btw, either via edgerc with extra parameter account-key(even though that still clutters edgerc) or via some alias list.

Usecase is being asked by a customer/colleague to purge some content quickly which now needs to be done via control-center or by having a list of API credentials for each customer which needs a lot of maintenance.