az keyvault secret show doesn't work with Key Vault Secrets User role

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**Related command**
az keyvault secret show

**Describe the bug**
It seems that the command always try to search for an access policy even if the keyvault is configured to use RBAC.

**To Reproduce**
Create a service principal
Create a keyvault using the RBAC mode (not the access policies)
Give the SP the Key Vault Secret User role
Create a secret
login with az cli using your SP
try to get the keyvaukt secret value with az cli

**Expected behavior**
The documentation should specify that only access policies are supported or the command should return the secret value.

**Environment summary**
Our tests was done on an azure devops agent in an AzureCli task. The service principal was configured using an Azure Devops Service Connection used by the AzureCli task.

**Additional context**