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="https://github.com/go-gitea/gitea/assets/32161460/2603504f-aee7-4929-a8c4-fb3412a7a0f6">

After:
<img width="1296" alt="image"
src="https://github.com/go-gitea/gitea/assets/32161460/58c03721-729f-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>

web_src/js/index.js

@@ -87,6 +87,7 @@ import {onDomReady} from './utils/dom.js';
 import {initRepoIssueList} from './features/repo-issue-list.js';
 import {initCommonIssueListQuickGoto} from './features/common-issue-list.js';
 import {initRepoContributors} from './features/contributors.js';
+import {initRepoCodeFrequency} from './features/code-frequency.js';
 import {initRepoDiffCommitBranchesAndTags} from './features/repo-diff-commit.js';
 import {initDirAuto} from './modules/dirauto.js';
 
@@ -177,6 +178,7 @@ onDomReady(() => {
   initRepository();
   initRepositoryActionView();
   initRepoContributors();
+  initRepoCodeFrequency();
 
   initCommitStatuses();
   initCaptcha();