feat(backup): Show BackupAppHighlightAlert after 2 flagship app open

By using localStorage to store the number of times the user open the
home app inside flagship app, we can very simply show
BackupAppHighlightAlert when user open flagship app for the second
time.

It also avoid to add code in flagship app.

src/components/AppHighlightAlert/BackupAppHighlightAlert.jsx

@@ -1,16 +1,77 @@
-import React from 'react'
+import React, { useEffect, useState } from 'react'
 
+import flag from 'cozy-flags'
+import { isFlagshipApp } from 'cozy-device-helper'
 import { useI18n } from 'cozy-ui/transpiled/react'
 
 import AppHighlightAlert from 'components/AppHighlightAlert/AppHighlightAlert'
 
+const APP_START_COUNT_KEY = 'BackupAppHighlightAlert__appStartCount'
+
+const MAX_COUNT_VALUE = 2
+const DISABLED_COUNT_VALUE = -1
+
+const useBackupAppHighlightAlert = () => {
+  const [
+    shouldShowBackupAppHighlightAlert,
+    setShouldShowBackupAppHighlightAlert
+  ] = useState(false)
+
+  useEffect(() => {
+    if (
+      !isFlagshipApp() ||
+      !flag('flagship.backup.enabled') ||
+      !flag('flagship.backup.homeHighlightEnabled')
+    ) {
+      return
+    }
+
+    const appStartCount = parseInt(
+      localStorage.getItem(APP_START_COUNT_KEY),
+      10
+    )
+
+    let newAppStartCount
+
+    if (isNaN(appStartCount)) {
+      newAppStartCount = 1
+    } else if (appStartCount === DISABLED_COUNT_VALUE) {
+      return
+    } else if (appStartCount < MAX_COUNT_VALUE) {
+      newAppStartCount = appStartCount + 1
+    } else {
+      newAppStartCount = DISABLED_COUNT_VALUE
+    }
+
+    localStorage.setItem(APP_START_COUNT_KEY, newAppStartCount.toString())
+
+    setShouldShowBackupAppHighlightAlert(newAppStartCount === 2)
+  }, [])
+
+  return [
+    shouldShowBackupAppHighlightAlert,
+    setShouldShowBackupAppHighlightAlert
+  ]
+}
+
 const BackupAppHighlightAlert = ({ apps }) => {
   const { t } = useI18n()
+  const [
+    shouldShowBackupAppHighlightAlert,
+    setShouldShowBackupAppHighlightAlert
+  ] = useBackupAppHighlightAlert()
+
+  const onClose = () => {
+    setShouldShowBackupAppHighlightAlert(false)
+  }
 
-  const onClose = () => {}
+  if (!shouldShowBackupAppHighlightAlert) {
+    return null
+  }
 
   return (
     <AppHighlightAlert
+      key="BackupAppHighlightAlert"
       apps={apps}
       appToHighlightSlug="photos"
       onClose={onClose}