Alerting: Extract methods for fetching rule groups with authorization (#75375)

* extract methods for fetching rule groups with authorization and refactor the request handlers.
* add logging to delete handler

pkg/services/ngalert/models/alert_rule.go

@@ -571,3 +571,15 @@ func RuleKeyFromContext(ctx context.Context) (AlertRuleKey, bool) {
 	key, ok := ctx.Value(ruleKeyContextKey{}).(AlertRuleKey)
 	return key, ok
 }
+
+// GroupByAlertRuleGroupKey groups all rules by AlertRuleGroupKey. Returns map of RulesGroup sorted by AlertRule.RuleGroupIndex
+func GroupByAlertRuleGroupKey(rules []*AlertRule) map[AlertRuleGroupKey]RulesGroup {
+	result := make(map[AlertRuleGroupKey]RulesGroup)
+	for _, rule := range rules {
+		result[rule.GetGroupKey()] = append(result[rule.GetGroupKey()], rule)
+	}
+	for _, group := range result {
+		group.SortByGroupIndex()
+	}
+	return result
+}