Add pagination to fork list (#17639)

- Resolves #14574
- Adds the necessary code to have pagination working in the forks list of
a repo. The code is mostly in par with the stars/watcher implementation.

templates/repo/forks.tmpl

@@ -18,5 +18,7 @@
 			{{end}}
 		</div>
 	</div>
+
+	{{ template "base/paginate" . }}
 </div>
 {{template "base/footer" .}}