Previews: datasource permissions (#52747)

* Previews: datasource permissions

* lint

* simplify - force non-null `ds_uids`

* add `canBeDisabled` to search service

* add `IncludeThumbnailsWithEmptyDsUids`

* remove force refresh migration

* refactor main preview service

* add safeguard

* revert ticker interval

* update testdata

* fix test

* add mock search service

* add datasources lookup test

* update migration

* extract ds lookup to its own package to avoid cyclic imports

* lint

* fix dashbaord extract, use the real datasource lookup in tests. IS IT BULLETPROOF YET?!

* fix dashbaord extract, use the real datasource lookup in tests. IS IT BULLETPROOF YET?!

* remove stale log

* consistent casing

* pass context to `createServiceAccount`

* filter out the special grafana ds

pkg/services/searchV2/testdata/search_response_frame.json

@@ -73,7 +73,7 @@
         "type": "other",
         "typeInfo": {
           "frame": "json.RawMessage",
-          "nullable": true
+          "nullable": false
         }
       },
       {
@@ -133,7 +133,7 @@
         ]
       ],
       [
-        null,
+        [],
         [
           "datasource-1"
         ],