Fix authentication configuration options

[m1so]

Description of your changes

Fixes #49 where authentication configuration options weren't propagated correctly, e.g.

provider "vault" {
  auth_login {
    path = "auth/approle/login"

    parameters = {
      role_id = "my-role"
    }
  }
}

is mapped to Kubernetes Secret as:

apiVersion: v1
kind: Secret
metadata:
  name: vault-creds
  namespace: vault
type: Opaque
stringData:
  approle-login: |
    {
      "auth_login": {
        "path": "auth/approle/login",
        "parameters": {"role_id": "my-role"}
      }
    }

but the contents of approle-login key needs to be internally passed to terraform.Setup{}.Configuration["auth_login"] as array of a single element, not as a map

see: https://registry.terraform.io/providers/hashicorp/vault/latest/docs#vault-authentication-configuration-options

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

1. make local-deploy
2. make uptest UPTEST_EXAMPLE_LIST=xyz.yaml
3. run ./cluster/test/setup-auth.sh to generate AppRole auth and role (Vault must be port-forwarded to :8200)
4. run any uptest example with ProviderConfig reference changed to vault-provider-config-approle

[sergenyalcin]

Thanks @m1so LGTM!

[github-actions]

Successfully created backport PR #51 for release-2.0.