Localize activity heatmap (except tooltip) (#24131)

The calculation of the total sum is moved to the backend so a full HTML
string could be sent.


![image](https://user-images.githubusercontent.com/20454870/232112381-c11d896b-ba47-40f8-b2a3-71cf4b3208de.png)

- Closes #10669
- 2nd attempt (the first was in #21570)

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Signed-off-by: Yarden Shoham <git@yardenshoham.com>
Co-authored-by: Giteabot <teabot@gitea.io>

options/locale/locale_en-US.ini

@@ -118,6 +118,12 @@ footer = Footer
 footer.software = About Software
 footer.links = Links
 
+[heatmap]
+number_of_contributions_in_the_last_12_months = %s contributions in the last 12 months
+no_contributions = No contributions
+less = Less
+more = More
+
 [editor]
 buttons.heading.tooltip = Add heading
 buttons.bold.tooltip = Add bold text