Add an Azure Postgres Flexible Server resource used by e2e tests

[Ferdinanddb]

As part of this issue that adds support to authenticate to a Postgres Flexible Server using managed identities, a Postgres Flexible Server resource is needed to run the e2e tests that will assert that the feature works as expected.

Use-Case

Create a module responsible for creating the Azure Postgres Flexible Server as well as other resources associated to it.

Specification

I would like to implement this feature. What I have in mind is the following:

Modification of the managed identities module

• Add a azurerm_user_assigned_identity that will be used by the e2e tests

Modification of the AKS module

• Add a azurerm_federated_identity_credential to map the newly created user assigned identity to the keda-operator Kubernetes service account.

New module for Azure Postgres Flexible Server

• Add a azurerm_postgresql_flexible_server,
• Add a azurerm_postgresql_flexible_server_active_directory_administrator to grant admin role to the newly created user assigned identity,
• Add a azurerm_postgresql_flexible_server_firewall_rule to allow access to all Azure IPs.
  • I am implementing it that way because the AKS cluster has an Azure IP, so I think it is the way to go, or maybe the range could be more specific? What do you think?
• Add a azurerm_postgresql_flexible_server_database
  • This database will be used by the e2e tests.

What do you think about this?