perf: cut MongoDB scans in repository workflows (#780)

* Add repository name index

* Optimize repository file counts

* Optimize MongoDB query workloads

src/core/model/anonymizedGists/anonymizedGists.schema.ts

@@ -14,7 +14,7 @@ const AnonymizedGistSchema = new Schema({
   anonymizeDate: Date,
   lastView: Date,
   pageView: Number,
-  owner: Schema.Types.ObjectId,
+  owner: { type: Schema.Types.ObjectId, index: true },
   conference: String,
   source: {
     gistId: String,