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>

options/locale/locale_en-US.ini

@@ -1919,6 +1919,7 @@ wiki.original_git_entry_tooltip = View original Git file instead of using friend
 activity = Activity
 activity.navbar.pulse = Pulse
 activity.navbar.contributors = Contributors
+activity.navbar.code_frequency = Code Frequency
 activity.period.filter_label = Period:
 activity.period.daily = 1 day
 activity.period.halfweekly = 3 days
@@ -2597,6 +2598,7 @@ component_loading = Loading %s...
 component_loading_failed = Could not load %s
 component_loading_info = This might take a bit…
 component_failed_to_load = An unexpected error happened.
+code_frequency.what = code frequency
 contributors.what = contributions
 
 [org]