feat: consider adding local cache to reduce impact on Azure APIs

[matt-FFFFFF]

A read of the standard ALZ library takes approximately 45 seconds. However repeated reads will trigger throttling by the azure policy api.

The built-in policies are read to:

1. Ensure they exist
2. Read metadata in referenced definitions in order to calculate the correct role assignments for DiNE/modify policies

We could cache these results to avoid the repeated reads from the api.

[richeney]

I assume that this is the throttling error? (In case anyone gets it and searches...)

│ Error: Failed to create/update resource
│
│   with module.management_groups.azapi_resource.policy_assignments["landingzones/Deploy-VM-Monitoring"],
│   on .terraform/modules/management_groups/main.policy_assignments.tf line 5, in resource "azapi_resource" "policy_assignments":
│    5: resource "azapi_resource" "policy_assignments" {
│
│ creating/updating Resource: (ResourceId "/providers/Microsoft.Management/managementGroups/landingzones/providers/Microsoft.Authorization/policyAssignments/Deploy-VM-Monitoring" / Api Version "2024-04-01"): GET
│ https://management.azure.com/providers/Microsoft.Management/managementGroups/landingzones/providers/Microsoft.Authorization/policyAssignments/Deploy-VM-Monitoring
│ --------------------------------------------------------------------------------
│ RESPONSE 429: 429 Too Many Requests
│ ERROR CODE: ResourceRequestsThrottled
│ --------------------------------------------------------------------------------
│ {
│   "error": {
│     "code": "ResourceRequestsThrottled",
│     "message": "Number of requests for Microsoft.Authorization exceeded the limit of '120' for time interval '00:01:00'. Please try again after '5' seconds."
│   }
│ }
│ --------------------------------------------------------------------------------

[matt-FFFFFF]

You can increase the number of retries here, using the azapi provider setting. Otherwise you can add ResourceRequestsThrottled to the retry configuration of the ALZ module