fix: ensure default values for resource_share_user and tags in main.tfvars.json

Author: mattdot

infra/main.tfvars.json

@@ -3,8 +3,8 @@
     "location": "${AZURE_LOCATION}",
     "use_billing_policy": "${USE_BILLING_POLICY:-false}",
     "azd_environment_name": "${AZURE_ENV_NAME}",
-    "resource_share_user": ${RESOURCE_SHARE_USER},
-    "tags": ${RESOURCE_TAGS},
+    "resource_share_user": ${RESOURCE_SHARE_USER:-[]},
+    "tags": ${RESOURCE_TAGS:-{}},
     "azure_ai_search_service_principal": {
         "client_id": "${AZURE_AI_SEARCH_SERVICE_PRINCIPAL_CLIENT_ID}",
         "enterprise_application_object_id": "${AZURE_AI_SEARCH_ENTERPRISE_APPLICATION_OBJECT_ID}",