Terraform: Add ServicePrincipals for two connectors

[paullatzelsperger]

In order for the fully-fledged end-to-end test to work, there must be two Azure AD service principals, one for the requesting connector (="client") and one for the providing connector (="provider").

The SP's must be configured such that the client can authenticate with the provider using OAuth2.

The creation of these SP's should be done in Terraform.