feat(repo): support search repository by topic name (#4505)

* feat(repo): support search repository by topic name

models/fixtures/repository.yml

@@ -407,3 +407,25 @@
   lower_name: utf8
   name: utf8
   is_private: false
+
+-
+  id: 34
+  owner_id: 21
+  lower_name: golang
+  name: golang
+  is_private: false
+  num_stars: 0
+  num_forks: 0
+  num_issues: 0
+  is_mirror: false
+
+-
+  id: 35
+  owner_id: 21
+  lower_name: graphql
+  name: graphql
+  is_private: false
+  num_stars: 0
+  num_forks: 0
+  num_issues: 0
+  is_mirror: false