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)

---------

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

web_src/js/components/ActivityHeatmap.vue

@@ -1,7 +1,7 @@
 <template>
   <div id="user-heatmap">
     <div class="total-contributions">
-      {{ sum }} contributions in the last 12 months
+      {{ locale.contributions_in_the_last_12_months }}
     </div>
     <calendar-heatmap
       :locale="locale"
@@ -41,15 +41,6 @@ export default {
     ],
     endDate: new Date(),
   }),
-  computed: {
-    sum() {
-      let s = 0;
-      for (let i = 0; i < this.values.length; i++) {
-        s += this.values[i].count;
-      }
-      return s;
-    }
-  },
   mounted() {
     // work around issue with first legend color being rendered twice and legend cut off
     const legend = document.querySelector('.vch__external-legend-wrapper');