Apply Slack's UI guide to channel placeholders

See https://slack.com/intl/en-de/help/articles/360017938993

Changelog: changed

app/assets/javascripts/integrations/edit/components/trigger_fields.vue

@@ -10,7 +10,7 @@ const typeWithPlaceholder = {
 };
 
 const placeholderForType = {
-  [typeWithPlaceholder.SLACK]: __('general, development'),
+  [typeWithPlaceholder.SLACK]: __('#general, #development'),
   [typeWithPlaceholder.MATTERMOST]: __('my-channel'),
 };
 

app/models/integrations/slack.rb

@@ -25,7 +25,7 @@ module Integrations
     end
 
     def default_channel_placeholder
-      _('general, development')
+      _('#general, #development')
     end
 
     def webhook_placeholder

locale/gitlab.pot

@@ -89,6 +89,9 @@ msgstr ""
 msgid "\"el\" parameter is required for createInstance()"
 msgstr ""
 
+msgid "#general, #development"
+msgstr ""
+
 msgid "%d Approval"
 msgid_plural "%d Approvals"
 msgstr[0] ""
@@ -38687,9 +38690,6 @@ msgid_plural "from %d jobs"
 msgstr[0] ""
 msgstr[1] ""
 
-msgid "general, development"
-msgstr ""
-
 msgid "group"
 msgstr ""
 

spec/frontend/integrations/edit/components/trigger_fields_spec.js

@@ -137,11 +137,11 @@ describe('TriggerFields', () => {
         const expectedResults = [
           {
             name: 'service[push_channel]',
-            placeholder: 'general, development',
+            placeholder: '#general, #development',
           },
           {
             name: 'service[merge_request_channel]',
-            placeholder: 'general, development',
+            placeholder: '#general, #development',
           },
         ];