Implement code frequency graph (#29191)

### Overview
This is the implementation of Code Frequency page. This feature was
mentioned on these issues: #18262, #7392.

It adds another tab to Activity page called Code Frequency. Code
Frequency tab shows additions and deletions over time since the
repository existed.

Before:
<img width="1296" alt="image"
src="2603504f-aee7-4929-a8c4-fb3412a7a0f6">

After:
<img width="1296" alt="image"
src="58c03721-729f-4536-a663-9f337f240963">

---

#### Features
- See additions deletions over time since repository existed
- Click on "Additions" or "Deletions" legend to show only one type of
contribution
- Use the same cache from Contributors page so that the loading of data
will be fast once it is cached by visiting either one of the pages

---------

Co-authored-by: Giteabot <teabot@gitea.io>
(cherry picked from commit 875f5ea6d83c8371f309df99654ca3556623004c)

web_src/js/utils.js

@@ -139,3 +139,5 @@ export function parseDom(text, contentType) {
 export function serializeXml(node) {
   return xmlSerializer.serializeToString(node);
 }
+
+export const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));