Adds tracking to create file button in widget

Adds Redis HLL tracking to the nothing to merge widget
states create file button.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/343126

app/assets/javascripts/vue_merge_request_widget/components/states/nothing_to_merge.vue

 <script>
 import { GlButton, GlSprintf, GlLink, GlSafeHtmlDirective } from '@gitlab/ui';
 import emptyStateSVG from 'icons/_mr_widget_empty_state.svg';
+import api from '~/api';
 import { helpPagePath } from '~/helpers/help_page_helper';
 
 export default {
@@ -22,6 +23,11 @@ export default {
   data() {
     return { emptyStateSVG };
   },
+  methods: {
+    onClickNewFile() {
+      api.trackRedisHllUserEvent('i_code_review_widget_nothing_merge_click_new_file');
+    },
+  },
   ciHelpPage: helpPagePath('/ci/quick_start/index.html'),
   safeHtmlConfig: { ADD_TAGS: ['use'] },
 };
@@ -59,6 +65,7 @@ export default {
             category="secondary"
             variant="success"
             data-testid="createFileButton"
+            @click="onClickNewFile"
           >
             {{ __('Create file') }}
           </gl-button>

config/metrics/aggregates/code_review.yml

@@ -67,6 +67,7 @@
     - 'i_code_review_user_resolve_conflict'
     - 'i_code_review_user_searches_diff'
     - 'i_code_review_user_resolve_thread_in_issue'
+    - 'i_code_review_widget_nothing_merge_click_new_file'
 - name: code_review_category_monthly_active_users
   operator: OR
   source: redis
@@ -126,6 +127,7 @@
     - 'i_code_review_user_resolve_conflict'
     - 'i_code_review_user_searches_diff'
     - 'i_code_review_user_resolve_thread_in_issue'
+    - 'i_code_review_widget_nothing_merge_click_new_file'
 - name: code_review_extension_category_monthly_active_users
   operator: OR
   source: redis

config/metrics/counts_28d/20211104154357_i_code_review_widget_nothing_merge_click_new_file_monthly.yml

+---
+key_path: redis_hll_counters.code_review.i_code_review_widget_nothing_merge_click_new_file_monthly
+description: Count of users who click the create file button in the nothing to merge widget state
+product_section: dev
+product_stage: create
+product_group: group::code review
+product_category: code_review
+value_type: number
+status: active
+milestone: '14.5'
+introduced_by_url:
+time_frame: 28d
+data_source: redis_hll
+instrumentation_class: RedisHLLMetric
+options:
+  events:
+    - i_code_review_widget_nothing_merge_click_new_file
+data_category: optional
+distribution:
+  - ce
+  - ee
+tier:
+  - free
+  - premium
+  - ultimate

config/metrics/counts_7d/20211104154352_i_code_review_widget_nothing_merge_click_new_file_weekly.yml

+---
+key_path: redis_hll_counters.code_review.i_code_review_widget_nothing_merge_click_new_file_weekly
+description: Count of users who click the create file button in the nothing to merge widget state
+product_section: dev
+product_stage: create
+product_group: group::code review
+product_category: code_review
+value_type: number
+status: active
+milestone: '14.5'
+introduced_by_url:
+time_frame: 7d
+data_source: redis_hll
+instrumentation_class: RedisHLLMetric
+options:
+  events:
+    - i_code_review_widget_nothing_merge_click_new_file
+data_category: optional
+distribution:
+  - ce
+  - ee
+tier:
+  - free
+  - premium
+  - ultimate

lib/gitlab/usage_data_counters/known_events/code_review_events.yml

@@ -249,3 +249,7 @@
   redis_slot: code_review
   category: code_review
   aggregation: weekly
+- name: i_code_review_widget_nothing_merge_click_new_file
+  redis_slot: code_review
+  category: code_review
+  aggregation: weekly