[BUG] EnvInjector pod does not support azure workload identity

[waterfoul]

Note: Make sure to check out known issues (https://akv2k8s.io/troubleshooting/known-issues/) before submitting

Components and versions
Select which component(s) the bug relates to with [X].

[ ] Controller, version: 1.5.0 (docker image tag)
[X] Env-Injector (webhook), version: 1.5.0 (docker image tag)
[ ] Other

Describe the bug
When the env injector (not the webhook) starts without the auth service it only supports VM identities and won't use azure workload identity. The issue arises on https://github.com/SparebankenVest/azure-key-vault-to-kubernetes/blob/master/cmd/azure-keyvault-env/authentication.go#L91 where it calls NewFromEnvironment without any way of using NewFromAzidentity

To Reproduce
Steps to reproduce the behavior:

1. Disable the auth service
2. Setup a pod with AZ Workload Identity
3. Start the pod
   Observe: The pod fails to find the identity

Expected behavior
The pod starts

Logs
If applicable, add logs to help explain your problem.

"failed to read secret from azure key vault" err="adal: Refresh request failed. Status Code = '400'. Response body: {\"error\":\"invalid_request\",\"error_description\":\"Identity not found\"} Endpoint http://169.254.169.254/metadata/identity/oauth2/token?api-version=2018-02-01&client_id=bb2edad4-2d5f-4e8a-a11f-b69d277ff284&resource=https%3A%2F%2Fvault.azure.net" 

Additional context
This does work with the auth service enabled and AUTH_TYPE "environment-azidentity". I propose the env injecotr pod gets it's own auth type env var (ENV_INJECTOR_AUTH_TYPE) with accepts "environment-azidentity" or "environment" (default)

[pzaj2]

@waterfoul Having the same scenario, did you manage to get it working in the end?

[phuc-nguyen2-ts]

Having the same issue with the error log exactly the same as you, would you be able to find a solution?