Add support for different Azure Cloud environments in event hub input

[jsoriano]

There are multiple Azure Cloud environments apart of the public cloud. In principle Filebeat supports custom endpoints in the connection_string, but there is at least a point where it uses the public cloud endpoints explicitly:

beats/x-pack/filebeat/input/azureeventhub/eph.go

Line 25 in d57bcf8

leaserCheckpointer, err := storage.NewStorageLeaserCheckpointer(cred, a.config.SAName, a.config.SAContainer, azure.PublicCloud)

Add support for the other environments. Not sure if this can be done automatically by guessing the environment from the endpoint in the connection_string. If not some additional setting will need to be added.

It may be needed to support loading environments from file for hybrid deployments. There is a EnvironmentFromFile() helper for that.

Reported in https://discuss.elastic.co/t/azure-module-error/227210

[elasticmachine]

Pinging @elastic/integrations-platforms (Team:Platforms)