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/components/RepoCodeFrequency.vue

@@ -0,0 +1,172 @@
+<script>
+import {SvgIcon} from '../svg.js';
+import {
+  Chart,
+  Legend,
+  LinearScale,
+  TimeScale,
+  PointElement,
+  LineElement,
+  Filler,
+} from 'chart.js';
+import {GET} from '../modules/fetch.js';
+import {Line as ChartLine} from 'vue-chartjs';
+import {
+  startDaysBetween,
+  firstStartDateAfterDate,
+  fillEmptyStartDaysWithZeroes,
+} from '../utils/time.js';
+import {chartJsColors} from '../utils/color.js';
+import {sleep} from '../utils.js';
+import 'chartjs-adapter-dayjs-4/dist/chartjs-adapter-dayjs-4.esm';
+
+const {pageData} = window.config;
+
+Chart.defaults.color = chartJsColors.text;
+Chart.defaults.borderColor = chartJsColors.border;
+
+Chart.register(
+  TimeScale,
+  LinearScale,
+  Legend,
+  PointElement,
+  LineElement,
+  Filler,
+);
+
+export default {
+  components: {ChartLine, SvgIcon},
+  props: {
+    locale: {
+      type: Object,
+      required: true
+    },
+  },
+  data: () => ({
+    isLoading: false,
+    errorText: '',
+    repoLink: pageData.repoLink || [],
+    data: [],
+  }),
+  mounted() {
+    this.fetchGraphData();
+  },
+  methods: {
+    async fetchGraphData() {
+      this.isLoading = true;
+      try {
+        let response;
+        do {
+          response = await GET(`${this.repoLink}/activity/code-frequency/data`);
+          if (response.status === 202) {
+            await sleep(1000); // wait for 1 second before retrying
+          }
+        } while (response.status === 202);
+        if (response.ok) {
+          this.data = await response.json();
+          const weekValues = Object.values(this.data);
+          const start = weekValues[0].week;
+          const end = firstStartDateAfterDate(new Date());
+          const startDays = startDaysBetween(new Date(start), new Date(end));
+          this.data = fillEmptyStartDaysWithZeroes(startDays, this.data);
+          this.errorText = '';
+        } else {
+          this.errorText = response.statusText;
+        }
+      } catch (err) {
+        this.errorText = err.message;
+      } finally {
+        this.isLoading = false;
+      }
+    },
+
+    toGraphData(data) {
+      return {
+        datasets: [
+          {
+            data: data.map((i) => ({x: i.week, y: i.additions})),
+            pointRadius: 0,
+            pointHitRadius: 0,
+            fill: true,
+            label: 'Additions',
+            backgroundColor: chartJsColors['additions'],
+            borderWidth: 0,
+            tension: 0.3,
+          },
+          {
+            data: data.map((i) => ({x: i.week, y: -i.deletions})),
+            pointRadius: 0,
+            pointHitRadius: 0,
+            fill: true,
+            label: 'Deletions',
+            backgroundColor: chartJsColors['deletions'],
+            borderWidth: 0,
+            tension: 0.3,
+          },
+        ],
+      };
+    },
+
+    getOptions() {
+      return {
+        responsive: true,
+        maintainAspectRatio: false,
+        animation: true,
+        plugins: {
+          legend: {
+            display: true,
+          },
+        },
+        scales: {
+          x: {
+            type: 'time',
+            grid: {
+              display: false,
+            },
+            time: {
+              minUnit: 'month',
+            },
+            ticks: {
+              maxRotation: 0,
+              maxTicksLimit: 12
+            },
+          },
+          y: {
+            ticks: {
+              maxTicksLimit: 6
+            },
+          },
+        },
+      };
+    },
+  },
+};
+</script>
+<template>
+  <div>
+    <div class="ui header gt-df gt-ac gt-sb">
+      {{ isLoading ? locale.loadingTitle : errorText ? locale.loadingTitleFailed: `Code frequency over the history of ${repoLink.slice(1)}` }}
+    </div>
+    <div class="gt-df ui segment main-graph">
+      <div v-if="isLoading || errorText !== ''" class="gt-tc gt-m-auto">
+        <div v-if="isLoading">
+          <SvgIcon name="octicon-sync" class="gt-mr-3 job-status-rotate"/>
+          {{ locale.loadingInfo }}
+        </div>
+        <div v-else class="text red">
+          <SvgIcon name="octicon-x-circle-fill"/>
+          {{ errorText }}
+        </div>
+      </div>
+      <ChartLine
+        v-memo="data" v-if="data.length !== 0"
+        :data="toGraphData(data)" :options="getOptions()"
+      />
+    </div>
+  </div>
+</template>
+<style scoped>
+.main-graph {
+  height: 440px;
+}
+</style>