Improve the CLI UX of `az acr update` and `az acr config` for registry configuration

ACR has two separate command groups for updating registry configuration — `az acr update` and `az acr config update` — which is confusing to users.

- `az acr config update` handles the registry's feature-wide policies (the policies section in ARM) — behavioral settings complex enough to warrant their own sub-commands with show and update.
- `az acr update` handles resource-level properties of the registry itself — updating the registry resource directly in ARM terms.

However,`az acr config update` looks like a subset of `az acr update` but actually isn't. Having two separate command groups to update registry properties is confusing. It's recommended to define a unified UX for registry's feature-wide policies and resource-level properties.

```
$ az acr show -n feynmanacr
{
"adminUserEnabled": true,
"anonymousPullEnabled": true,
"autoGeneratedDomainNameLabelScope": "Unsecure",
"creationDate": "2022-06-19T14:28:34.052126+00:00",
"dataEndpointEnabled": false,
"dataEndpointHostNames": [],
"encryption": {
"keyVaultProperties": null,
"status": "disabled"
},
"id": "/subscriptions/0518b2a2-73e3-4d90-b20b-a3d8cf7a7a3d/resourceGroups/myResourceGroup/providers/Microsoft.ContainerRegistry/registries/feynmanacr",
"identity": {
"principalId": "f4fa0e52-0b8d-42b6-941e-f7b3606df7f6",
"tenantId": "72f988bf-86f1-41af-91ab-2d7cd011db47",
"type": "systemAssigned",
"userAssignedIdentities": null
},
"location": "eastus",
"loginServer": "feynmanacr.azurecr.io",
"metadataSearch": "Disabled",
"name": "feynmanacr",
"networkRuleBypassOptions": "AzureServices",
"networkRuleSet": {
"defaultAction": "Allow",
"ipRules": []
},
"policies": {
"azureAdAuthenticationAsArmPolicy": {
"status": "enabled"
},
"exportPolicy": {
"status": "enabled"
},
"quarantinePolicy": {
"status": "disabled"
},
"retentionPolicy": {
"days": 7,
"lastUpdatedTime": "2025-08-26T01:21:16.288964+00:00",
"status": "enabled"
},
"softDeletePolicy": {
"lastUpdatedTime": "2025-11-21T22:39:25.781713+00:00",
"retentionDays": 7,
"status": "enabled"
},
"trustPolicy": {
"status": "disabled",
"type": "Notary"
}
},
"privateEndpointConnections": [],
"provisioningState": "Succeeded",
"publicNetworkAccess": "Enabled",
"resourceGroup": "myResourceGroup",
"roleAssignmentMode": "LegacyRegistryPermissions",
"sku": {
"name": "Premium",
"tier": "Premium"
},
"status": null,
"systemData": {
"createdAt": "2022-06-19T14:28:34.052126+00:00",
"createdBy": "demo@test.com",
"createdByType": "User",
"lastModifiedAt": "2025-11-21T22:39:25.738070+00:00",
"lastModifiedBy": "demo@test.com",
"lastModifiedByType": "User"
},
"tags": {},
"type": "Microsoft.ContainerRegistry/registries",
"zoneRedundancy": "Disabled"
}
```

Start by comparing the current `az acr update` and `az acr config update` command groups with the registry properties and feature-wide policies shown in the `az acr show` output. Define a unified command UX that clearly separates or combines those responsibilities, then verify that the resulting commands consistently cover both resource-level properties and feature-wide policies.

Written by the indexing model from the issue text.