Annotations/Alerting: Add Loki historian store stub (#78363)

* Add Loki historian store stub

* Add composite store

* Use composite store if Loki historian enabled

* Split store interface into read/write

* Make composite + historian stores read only

* Use variadic constructor for composite

* Modify Loki store enable logic

* Use dskit.concurrency.ForEachJob for parallelism

pkg/services/annotations/models.go

@@ -44,6 +44,21 @@ type TagsDTO struct {
 	Count int64  `json:"count"`
 }
 
+// sort tags in ascending order by tag string
+type SortedTags []*TagsDTO
+
+func (s SortedTags) Len() int {
+	return len(s)
+}
+
+func (s SortedTags) Less(i, j int) bool {
+	return s[i].Tag < s[j].Tag
+}
+
+func (s SortedTags) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}
+
 // FindTagsResult is the result of a tags search.
 type FindTagsResult struct {
 	Tags []*TagsDTO `json:"tags"`
@@ -110,6 +125,24 @@ type ItemDTO struct {
 	Data         *simplejson.Json `json:"data"`
 }
 
+type SortedItems []*ItemDTO
+
+// sort annotations in descending order by end time, then by start time
+func (s SortedItems) Len() int {
+	return len(s)
+}
+
+func (s SortedItems) Less(i, j int) bool {
+	if s[i].TimeEnd != s[j].TimeEnd {
+		return s[i].TimeEnd > s[j].TimeEnd
+	}
+	return s[i].Time > s[j].Time
+}
+
+func (s SortedItems) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}
+
 type annotationType int
 
 const (